Glossary of medicine

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  • ABO blood groups - The system by which human blood is classified, based on proteins occurring on red blood cells; the four classification groups are A, AB, B, and O
  • ACE inhibitor - a drug typically used to treat high blood pressure (Angiotensin-Converting
  • AIDS-related complex - symptoms including weight loss, fever, and enlarged lymph nodes experienced by people who are infected with HIV but do not yet have AIDS
  • AIDS - see Acquired immunodeficiency syndrome
  • ALS - see Amyotrophic lateral sclerosis
  • ARC - see AIDS-related complex
  • Abdominal cavity - the part of the body between the bottom of the ribs and the top of the thighs, containing most of the digestive and urinary systems along with some reproductive organs
  • Abortion - termination of a pregnancy; can occur because of natural causes (called a miscarriage) or be a medical intervention
  • Abscess - an accumulation of pus in a body tissue, usually caused by a bacterial infection
  • Achilles tendon - the tendon at the back of the lower leg that connects the calf muscle to the heel bone
  • Acid reflux - a disorder in which acid in the stomach comes up into the esophagus, because the valve separating the stomach and esophagus does not function properly
  • Acid-base balance - the mechanisms that the body uses to keep its fluids close to neutral (neither basic nor acidic) so that the body can function properly
  • Acidosis - a condition marked by abnormally high acid levels in the blood, associated with some forms of diabetes, lung disease, and severe kidney disease
  • Acne - a skin condition characterized by inflamed, pus-filled areas that occur on the skin's surface, most commonly occurring during adolescence
  • Acquired immunodeficiency syndrome - infection by the human immunodeficiency virus (HIV), which causes a weakening of the immune system
  • Acquired - a word describing any condition that is not present at birth, but develops some time during life
  • Acute respiratory disease - an urgent condition in which oxygen levels in the blood are lower than normal and breathing is difficult
  • Acute - describes a condition or illness that begins suddenly and is usually short-lasting
  • Addiction - dependence on a substance (such as alcohol or other drugs) or an activity, to the point that stopping is very difficult and causes severe physical and mental reactions
  • Adenitis - infection and inflammation of a gland, especially a lymph node
  • Adipose tissue - another term for fatty tissue; it stores energy, insulates, and cushions the body
  • Adjuvant therapy - the use of drugs or radiation therapy in the treatment of cancer along with surgery
  • Adrenal failure - a condition in which the adrenal glands do not produce enough of the hormones that control important functions such as blood pressure
  • Adrenal glands - two small glands located on top of the kidneys that secrete several important hormones into the blood
  • Adverse reaction - an unintended and unwanted side effect of some sort of treatment, usually drug therapy
  • Aerobic exercise - physical activity during which the heart and lungs must work harder to meet the body's increased oxygen demand
  • Affective disorder - a mental disorder involving abnormal moods and emotions; affective disorders include manic-depressive disorder
  • Afterbirth - the placenta and membranes that are eliminated from the woman's uterus following the birth of a child
  • Afterpains - normal contractions of the uterus after childbirth that usually occur for the first few days after delivery
  • Air embolism - the blockage of an artery by air bubbles, which may have entered during surgery or after an injury
  • Airway obstruction - blockage of the passage of air through the windpipe to the lungs
  • Airways - the passageways that air moves through while traveling in and out of the lungs during breathing
  • Albinism - a condition in which people are born with insufficient amounts of the pigment melanin, which is responsible for hair, skin, and eye color
  • Alcoholic cardiomyopathy - heart damage and failure caused by intake of too much alcohol
  • Alimentary canal - another term for the digestive tract
  • Alkalosis - dangerously decreased acidity of the blood, which can be caused by high altitudes, hyperventilation, and excessive vomiting
  • Alkylating agents - substances used in cancer treatment that interfere with the division of cells
  • Allergen - a substance that causes an allergic reaction
  • Allergic rhinitis - irritation of the nasal passages and the whites of the eyes, causing sneezing, runny nose, and sore eyes
  • Allergy - a negative reaction to a substance that in most people causes no reaction
  • Alopecia - baldness or loss of hair, mainly on the head, either in defined patches or completely; the cause is unknown
  • Altitude sickness - headaches, dizziness, and nausea usually experienced at heights above 8,000 ft because of reduced oxygen in the air
  • Alzheimer disease - a condition that occurs late in life and worsens with time in which brain cells degenerate; it is accompanied by memory loss, physical decline, and confusion
  • Amenorrhea - absence of menstrual periods, occurring either after or before menstruation has begun
  • Amniocentesis - a procedure in which a small amount of amniotic fluid is removed from the mother’s womb in order to detect abnormalities of the fetus
  • Amniotic fluid - clear fluid that surrounds a fetus during pregnancy and cushions and protects it
  • Amyotrophic lateral sclerosis - the most common of a group of disorders known as motor neuron diseases, in which the nerves in the brain that control the movement of muscles degenerate and muscle function is gradually lost; commonly called Lou Gehrig's disease
  • Anabolic steroid - a drug similar to the male hormone testosterone that builds muscles and strengthens bones, but has adverse side effects
  • Anal fissure - a long, open sore on the skin of the anus
  • Anal fistula - an abnormal tubelike passage connecting the anus to the surface of the surrounding skin
  • Anal sphincter - a ring of muscle fibers at the opening of the rectum, controlling the opening and closing of the anus
  • Analgesic - a drug that relieves pain, such as aspirin or acetaminophen
  • Anaphylactic shock - a life-threatening allergic reaction resulting in difficulty breathing and low blood pressure
  • Anatomy - the structure of bodies; commonly refers to the study of body structure
  • Androgen - a hormone (such as testosterone) that causes development of male characteristics and sex organs
  • Anemia - a condition in which the blood does not contain enough hemoglobin, the compound that carries oxygen from the lungs to other parts of the body
  • Anencephaly - a fatal birth defect in which the brain and spinal cord have failed to develop, resulting in the absence of a portion of the skull and brain
  • Anesthesia - a loss of sensation in a certain part of the body or throughout the body
  • Anesthetic - a substance that temporarily causes a person to be unable to feel pain, either in a certain area or over the entire body
  • Aneurysm - an abnormal swelling of the wall of an artery, caused by a weakening in the vessel wall
  • Angina pectoris - pain experienced in the chest, arms, or jaw because of a lack of oxygen to the heart muscle
  • Angioma - a tumor made of blood vessels or lymph vessels that is not cancerous
  • Angioplasty - the use of surgery to make a damaged blood vessel function properly again; may involve widening or reconstructing the blood vessel
  • Anorexia nervosa - a dangerous eating disorder mainly affecting young girls in which the sufferer has an intense fear of looking fat, avoids food, and loses weight excessively
  • Antacid - a drug that neutralizes stomach acids; used to treat indigestion, heartburn, and acid reflux
  • Antibiotic resistance - the development by bacteria of the ability to live in the presence of a certain antibiotic, making treatment difficult
  • Antibiotics - bacteria-killing substances that are used to fight infection
  • Antibody - a protein made by white blood cells that reacts with a specific foreign protein as part of the immune response
  • Anticoagulants - drugs used to stop abnormal blood clotting, such as to prevent stroke
  • Antiemetics - drugs used to treat nausea and vomiting
  • Antihistamine - a drug that relieves an allergic reaction by stopping the effects of histamine, the substance responsible for the negative symptoms associated with the reaction
  • Antihypertensives - drugs used to relieve the symptoms and prevent the damage that can occur from high blood pressure
  • Antioxidants - substances that protect against cell damage by guarding the cell from oxygen free radicals
  • Antipsychotics - drugs used to treat severe mental disorders
  • Antiseptics - chemicals applied to the skin that prevent infection by killing bacteria and other harmful organisms
  • Anus - the opening through which feces are passed from the body
  • Aorta - the main artery in the body, carrying oxygenated blood from the heart to other arteries in the body
  • Aortic stenosis - narrowing of the opening of the aortic valve in the heart, which increases resistance to blood flow from the left ventricle to the aorta; commonly a birth defect or caused by scarring and calcium accumulation in the valve from rheumatic fever
  • Apgar score - a system for evaluating the health of a newborn baby; rated on a scale of 0- 10
  • Aplasia - the complete or partial failure of any organ or tissue to grow
  • Aplastic anemia - a severely reduced number of red blood cells, white blood cells, and platelets
  • Apnea - a possibly life-threatening condition in which breathing stops, for either a short or long period of time
  • Appendectomy - surgical removal of the appendix to treat appendicitis
  • Appendicitis - inflammation of the appendix
  • Appendix - a short, tubelike structure that branches off the large intestine; does not have any known function
  • Arteriosclerosis - a disorder causing thickening and hardening of artery walls
  • Arteritis - inflammation of the walls of an artery that causes the passageway to become narrower; can lead to tissue damage because oxygen is not properly supplied
  • Artery - a large blood vessel that carries blood from the heart to tissues and organs in the body
  • Arthritis - a disease of the joints characterized by inflammation, pain, stiffness, and redness
  • Arthroscopy - a procedure used to examine the inside of a joint using a viewing tube (an endoscope)
  • Artificial insemination - injection of semen into the cervix
  • Artificial respiration/ventilation - the forcing of air (either by mouth-to-mouth or mouthto-nose means) into the lungs of a person who has stopped breathing
  • Ascites - excess fluid in the abdominal cavity, which leads to swelling
  • Ascorbic acid - the chemical term for vitamin C
  • Aspermia - the failure either to produce or to ejaculate sperm
  • Asphyxia - the medical term for suffocation; can be caused by choking on an object, by lack of oxygen in the air, or by chemicals such as carbon monoxide, which reduce the amount of oxygen in the blood
  • Asthma - a disorder characterized by inflamed airways and difficulty breathing
  • Astigmatism - a disorder in which the front surface of the eye (the cornea) is not correctly spherical, resulting in blurry vision
  • Atherectomy - a procedure performed to remove plaque that is blocking an artery
  • Atheroma - fatty deposits on the inner walls of blood vessels, which can cause narrowing and decrease blood flow
  • Atherosclerosis - narrowing of the lining of the arteries due to the accumulation of fat and other materials; leads to coronary heart disease, stroke, and other disorders
  • Athlete's foot - an infection between the toes caused by a fungus, which leads to sore, cracked, and peeling skin
  • Atresia - a birth defect in which a normal body opening or canal is absent; usually requires surgical repair soon after birth
  • Atria - the two upper chambers of the heart; the singular form is atrium
  • Atrial fibrillation - an irregular heartbeat in which the upper chambers of the heart (the atria) beat inconsistently and rapidly
  • Atrial flutter - an irregular heartbeat in which the upper chambers of the heart (the atria) beat rapidly but consistently
  • Atrial septal defect - a hole located in the wall between the two upper chambers of the heart
  • Atrophy - the shrinkage or near disappearance of a tissue or organ
  • Attention-deficit disorder - a disorder mainly present in children and adolescents, characterized by learning and behavior problems, inability to pay attention, and sometimes hyperactivity
  • Audiogram - a graph showing a person's hearing ability, determined from a set of tests examining hearing acuity of different sound frequencies
  • Aura - a "warning" signal that comes before a migraine headache or an epileptic seizure, which might include emotions or sensations of movement or discomfort
  • Auscultation - the act of listening to sounds within the body, such as the heartbeat, with a stethoscope
  • Autism - a mental disorder characterized by an inability to relate to other people and extreme withdrawal
  • Autoimmune disease - a disorder in which the body’s immune system attacks itself
  • Autonomic nervous system - the part of the nervous system that controls automatic body functions, such as heart rate, sweating, pupil dilation, and digestion; divided into the sympathetic nervous system and the parasympathetic nervous system
  • Autopsy - the examination of a body following death, possibly to determine the cause of death or for research
  • Autosomal dominant - a term describing a gene on any chromosome other than the sex chromosomes that produces its effect whenever it is present; can also describe the effect of the gene itself
  • Autosomal recessive - a term used to describe a gene on any chromosome other than the sex chromosomes that produces its effect only when two copies of it are present; can also describe the effect of the gene itself
  • Axilla - medical term for the armpit
  • B cell - a white blood cell that makes antibodies to fight infections caused by foreign proteins
  • B lymphocyte - a type of white blood cell that makes antibodies and is an important part of the immune response
  • BCG vaccine - a vaccine used to protect against tuberculosis
  • Bacillus - any bacteria that is rod-shaped; responsible for diphtheria, dysentery, tetanus, and tuberculosis, as well as other diseases
  • Bacteremia - a condition in which bacteria are present in the bloodstream; may occur after minor surgery or infection and may be dangerous for people with a weakened immune system or abnormal heart valves
  • Bacteriostatic - term used to describe a substance that stops the growth of bacteria (such as an antibiotic)
  • Bacterium - a tiny, single-celled microorganism, commonly known as a germ; some bacteria, called pathogens, cause disease
  • Bacteriuria - bacteria in the urine; large amounts can indicate bladder, urethra, or kidney infection
  • Ball-and-socket joint - a joint consisting of a ball-shaped bone that fits into a cup-shaped bone, making the joint free to rotate; examples include the hip and shoulder
  • Balloon angioplasty - a technique that uses a balloon catheter to open arteries clogged with fatty deposits
  • Balloon catheter - a hollow tube with a small, inflatable balloon at the tip; used to open a narrowed artery or organ that has become blocked
  • Barbiturates - a group of sedatives that reduce activity in the brain; are habit-forming and are possibly fatal when taken with alcohol
  • Barium enema - a technique in which barium is placed into the large intestine and rectum and then X-rays are taken to check for possible disorders of these organs
  • Barrier method of contraception - a birth-control technique using a condom, diaphragm, or another similar device to block the path of sperm to an egg
  • Bartholin's glands - two pea-sized glands that, when sexually aroused, release a fluid that lubricates the vagina
  • Basal cell carcinoma - a type of skin cancer that is caused by exposure to large amounts of sunlight; commonly found on the neck, face, and arms
  • Basal metabolic rate - the lowest rate at which a person can possibly use energy and remain alive; at this rate, only absolutely necessary functions such as breathing are maintained
  • Becker’s muscular dystrophy - a hereditary disease in which the muscles weaken and waste away; similar to Duchenne muscular dystrophy but starts later in life and advances more slowly
  • Bell's palsy - another name for facial palsy, the usually one-sided, temporary numbing of the facial muscles, caused by an inflamed nerve
  • Bends - see Decompression sickness
  • Benign tumor - a tumor that is not cancerous, which means it does not spread through the body, but may grow and become dangerous
  • Beta blocker - a type of drug used to treat high blood pressure and heart disorders by reducing the strength and rate of the pumping by the heart
  • Beta carotene - a pigment found in orange vegetables and fruits, which the body converts to vitamin A; possibly protects against cancer
  • Bifocal - a lens that corrects both near and distant vision by having two parts with different focusing strengths
  • Bilateral - a term describing a condition that affects both sides of the body or two paired organs, such as bilateral deafness (deafness in both ears)
  • Bile duct - a tube that carries bile from the liver to the gallbladder and then to the small intestine
  • Bile - a yellow-green liquid produced in the liver whose function is to remove waste from the liver and break down fats as food is digested
  • Biliary atresia - a birth defect in which the bile ducts are not completely developed; often a liver transplant is necessary
  • Biliary colic - a severe pain in the upper right section of the abdomen, usually caused by a gallstone passing out of the bladder or through the bile ducts
  • Biliary tract - the system of organs and ducts through which bile is made and transported from the liver to the small intestine
  • Bilirubin - the orange-yellow pigment in bile, causing jaundice if it builds up in the blood and skin; the levels of bilirubin in the blood are used to diagnose liver disease
  • Binging and purging - behavior characteristic of the disorder bulimia in which a person overeats then rids themselves of the food before it can be absorbed by the body, either by forced vomiting or through the use of laxatives
  • Biochemistry - the science that studies the chemistry of living organisms, including humans
  • Bioequivalent - a drug that has the same effect on the body as another drug
  • Biofeedback - a technique used to gain control over a function that is normally automatic (such as blood pressure or pulse rate); the function is monitored and relaxation techniques are used to change it to a desired level
  • Bipolar disorder - an illness in which the patient goes back and forth between opposite extremes; the most notable bipolar disorder is manic-depressive disorder, which is characterized by extreme highs and lows in mood
  • Birth canal - the passage that includes the uterus and vagina through which the baby passes at birth
  • Birth control - the regulation of the number of children born, referring either to the prevention of pregnancy (by birth control pill, sterilization, etc) or the prevention of birth (by abortion, etc)
  • Birth defect - an abnormality that is present when a baby is born
  • Birthmark - any area of discolored skin that is present when a baby is born
  • Bisexuality - sexual interest in members of both sexes
  • Bladder - an organ located in the pelvis whose function is to collect and store urine until it is expelled
  • Blepharitis - inflammation of the eyelids
  • Blind spot - a spot in the field of vision that is not sensitive to light; it is a product of the entrance of the optic nerve into the eyeball, where no light receptors are present on the retina
  • Blood clot - a semisolid mass of blood that forms to help seal and prevent bleeding from a damaged vessel
  • Blood poisoning - see Septicemia
  • Blood pressure - the tension in the main arteries that is created by the beating of the heart and the resistance to flow and elasticity of the blood vessels
  • Blood transfusion - the transfer of blood or any of its parts to a person who has lost blood due to an injury, disease, or operation
  • Blood type - a category used to describe a person's blood according to the kinds of proteins present on the surface of the red blood cells
  • Blood-brain barrier - a layer of tightly bound cells that prevents certain substances carried in the bloodstream from entering the brain
  • Boil - an inflamed, raised area of skin that is pus-filled; usually an infected hair follicle
  • Bone marrow transplant - a surgical procedure in which defective or cancerous bone marrow is replaced with healthy marrow, either from the patient or a donor
  • Bone marrow - the fatty yellow or red tissue inside bones that is responsible for producing blood cells
  • Bone spur - an abnormal growth of bone out of another bone, often located on the heel and usually painful
  • Booster - an additional dose of a vaccine taken after the first dose to maintain or renew the first one
  • Botulism - poisoning from poorly preserved food contaminated with a dangerous bacterial toxin that results in paralysis
  • Bowel - see Intestine
  • Bradycardia - a slow heart rate, usually below 60 beats per minute in adults
  • Brain damage - permanent death or damage of brain cells resulting in decreased mental ability
  • Brain death - the condition in which the brain stops functioning while the heart continues to beat
  • Breech birth - childbirth in which the baby is turned around in the uterus and emerges head-last instead of head-first
  • Bronchiolitis - an infection caused by a virus in the bronchioles (the smallest airways in the lungs), mainly affecting young children
  • Bronchitis - inflammation of the bronchial tubes, which connect the trachea to the lungs
  • Bronchoconstrictor - a substance that causes the lung airways to tighten up and become more narrow
  • Bronchodilator - a drug that widens the airways in the lungs to improve breathing; works by relieving muscle contraction or buildup of mucus
  • Bronchospasm - the temporary narrowing of the airways in the lungs, either as a result of muscle contraction or inflammation; may be caused by asthma, infection, lung disease, or an allergic reaction
  • Bruise - see Contusion
  • Bruxism - an unaware clenching or grinding of the teeth, usually during sleep
  • Bubonic plague - a form of plague in which lymph nodes in the groin and armpit swell
  • Bulimia - a disorder in which a person eats large amounts of food then forces vomiting or uses laxatives to prevent weight gain (called binging and purging)
  • Bunion - a hard, fluid-filled pad along the inside joint of the big toe; may be caused by wearing high-heeled shoes or a genetically weak joint
  • Burkitt's lymphoma - a cancer of lymph tissue that most frequently occurs in the abdomen, the ovaries, and the bones of the face; it is associated with malaria
  • Bursa - a fluid-filled sac that cushions and reduces friction in certain parts of the body
  • Bursitis - inflammation of a bursa due to excessive pressure or friction, or from injury
  • Butterfly bandage - a butterfly-shaped bandage that can help close a minor cut for proper healing
  • Bypass - a surgical technique in which the flow of blood or another body fluid is redirected around a blockage
  • CAT scanning - see Computed tomography scanning
  • CNS - see Central nervous system
  • CPR - see Cardiopulmonary resuscitation
  • CT scanning - a procedure that uses X-rays and computers to create cross-sectional images of the body to diagnose and monitor disease
  • CVS - see Chorionic villus sampling
  • Calcification - the depositing of calcium salts in the body, which occurs normally in teeth and bones but abnormally in injured muscles and narrowed arteries
  • Calcitonin - a hormone made in the thyroid gland that controls calcium levels in the blood by slowing the loss of calcium from bones; used to treat hypercalcemia (excess calcium in the blood)
  • Calcium channel blocker - a drug used to treat chest pain, high blood pressure, and irregular heartbeat by preventing the movement of calcium into the muscle
  • Calcium - a plentiful mineral in the body and the basic component of teeth and bones; essential for cell function, muscle contraction, transmission of nerve impulses, and blood clotting
  • Callus - a thickened area of skin due to consistent pressure or friction, or the area around a bone break where new bone is formed
  • Calorie - a unit that is used to measure the energy content in food
  • Canal - a tunnel-like passage
  • Cancer staging - a method to determine how much a cancer has developed
  • Cancer - a group of diseases in which cells grow unrestrained in an organ or tissue in the body; can spread to tissues around it and destroy them or be transported through blood or lymph pathways to other parts of the body
  • Candidiasis - a yeast infection caused by the fungus Candida albicans; occurs most often in the vagina, but also in the mouth, on moist skin, or on the penis
  • Canker sore - small, painful sore that usually occurs on the inside of the lip or cheek, or sometimes under the tongue; caused by bacteria, irritation of the area, stress, or allergies
  • Capillary - a tiny blood vessel that connects the smallest arteries to the smallest veins and allows exchange of oxygen and other materials between blood cells and body tissue cells
  • Carbohydrate - a substance, mainly sugar and starch, that is a main source of energy for the body and is found in sources such as cereals, breads, pastas, grains, and vegetables
  • Carbon dioxide - a colorless, odorless gas present in small amounts in the atmosphere and formed during respiration
  • Carcinogen - anything that can cause cancer
  • Carcinoma - a cancer that occurs on the surface or lining of an organ
  • Cardiac arrest - the sudden cessation of the heart's pumping action, possibly due to a heart attack, respiratory arrest, electrical shock, extreme cold, blood loss, drug overdose, or a severe allergic reaction
  • Cardiogenic shock - a severely dangerous condition involving decreased blood output from the heart, usually as a result of a heart attack
  • Cardiomegaly - a condition marked by enlargement of the heart, either because of a thickened heart muscle or an enlarged heart chamber; usually a result of the heart having to work harder than normal, as occurs with high blood pressure
  • Cardiomyopathy - a disease of the heart muscle that results in decreased output and reduced blood flow
  • Cardiopulmonary resuscitation - the administration of heart compression and artificial respiration to restore circulation and breathing
  • Cardiovascular system - the heart and blood vessels that are responsible for circulating blood throughout the body
  • Carditis - inflammation of the heart
  • Carotene - an orange pigment present in colored plants such as carrots that is converted by the body to the essential nutrient vitamin A
  • Carotid arteries - four main arteries that carry blood to the head and neck
  • Carpal bones - eight bones that together make the wrist
  • Carpal tunnel syndrome - a condition in which pressure on the median nerve in the wrist causes soreness, tingling, and numbness in the thumb and index and middle fingers
  • Cartilage - a connective tissue (softer than bone) that is part of the skeletal system, including the joints
  • Cast - a hard plaster or fiberglass shell that molds to a body part such as an arm and holds it in place for proper healing
  • Cat-scratch fever - an illness transmitted to humans through a cat's bite or scratch, which is thought to be caused by an unidentified bacteria; characterized by a swollen lymph node or blister near the bite or scratch, fever, rash, and headache; most commonly occurring in children
  • Cataract - a disorder in which the lens of the eye becomes less transparent and in some cases a milky white, making vision less clear
  • Catheter - a hollow, flexible tube inserted into the body to put in or take out fluid, or to open up or close blood vessels
  • Catheterization - a technique in which a hollow, flexible tube is used to drain body fluids (such as urine), to introduce fluids into the body, or to examine or widen a narrowed vein or artery
  • Cauliflower ear - a deformed ear caused by repeated injury
  • Cauterization - the use of heat, an electric current, or a chemical to destroy tissue or stop bleeding
  • Cecum - the beginning of the large intestine, which is connected to the appendix at its lower end
  • Cell - the tiny structures that make up all the tissues of the body and carry out all of its functions
  • Cellulitis - a skin infection caused by bacteria (usually streptococci); can lead to tissue damage and blood poisoning if untreated; characterized by fever, chills, heat, tenderness, and redness
  • Central nervous system - the brain and spinal cord
  • Cerebellum - a region of the brain located at the back; responsible for coordination of movement and maintaining balance
  • Cerebral palsy - a group of disorders of movement and posture resulting from damage to the brain early in a child's development; causes muscle weakness, difficulty coordinating voluntary movements, and sometimes complete loss of motion
  • Cerebrospinal fluid - a clear, watery fluid circulating in and around the brain and spinal column, which contains glucose, proteins, and salts for nutrition
  • Cerebrovascular disease - a disease affecting any artery supplying blood to the brain; may cause blockage or rupture of a blood vessel, leading to a stroke
  • Cerebrum - the largest part of the brain and the site of most of its activity, including sensory and motor functions
  • Cervical cap - a small rubber cup that is placed tightly over the cervix to prevent pregnancy
  • Cervical dysplasia - changes that occur in the cells on the surface of the cervix that usually precede the stages of cancer
  • Cervical incompetence - a weakness of the neck of the uterus, which can lead to spontaneous abortion due to an inability to support the weight of the fetus
  • Cervical smear - a procedure in which cells are scraped off of the cervix and examined to detect changes that might precede the stages of cancer; also called a Pap smear
  • Cervicitis - inflammation of the cervix
  • Cervix - a small, round organ making up the neck of the uterus and separating it from the vagina
  • Cesarean section - an operation performed to remove a fetus by cutting into the uterus, usually through the abdominal wall
  • Chancre - a painless sore that has a thick, rubbery base and a defined edge; usually occurs on the genitals after the contraction of the sexually transmitted disease syphilis
  • Chemotherapy - the treatment of infections or cancer with drugs that act on diseaseproducing organisms or cancerous tissue; may also affect normal cells
  • Chickenpox - a contagious disease that causes a rash and a fever; most commonly occurs during childhood
  • Chlamydia - microorganisms that cause several human infections and can be transmitted sexually
  • Cholecystectomy - the surgical removal of the gallbladder
  • Cholera - a bacterial infection of the small intestine that causes severe watery diarrhea, dehydration, and possibly death
  • Cholesterol - a substance in body cells that plays a role in the production of hormones and bile salts and in the transport of fats in the bloodstream
  • Chondritis - inflammation of cartilage
  • Chondroma - a noncancerous tumor that occurs in cartilage
  • Chondromalacia patellae - painful damage to the cartilage behind the kneecap
  • Chondrosarcoma - a cancerous cartilage tumor that develops inside of bone or on its surface
  • Chorionic villus sampling - a method of diagnosing fetal defects in which a small amount of tissue is taken from the placenta and analyzed for abnormalities
  • Choroiditis - inflammation of the blood vessels behind the retina that line the back of the eye
  • Chromosome analysis - examination of a person’s chromosomes either to determine if that person has an abnormality or to investigate one
  • Chronic obstructive lung disease - a combination of the lung diseases emphysema and bronchitis, characterized by blockage of airflow in and out of the lungs
  • Chronic - describes a disorder that continues for a long period of time
  • Cilia - tiny, hairlike structures on the outside of some cells, providing mobility
  • Circumcision - the surgical removal of the foreskin of the penis
  • Cirrhosis of the liver - gradual loss of liver function due to cell damage and internal scarring
  • Claudication - a cramping pain in one or both legs while walking, which can cause limping
  • Claustrophobia - fear of being confined in an enclosed or crowded space
  • Clavicle - the medical term for the collarbone
  • Cleft lip - a birth defect in which the upper lip is split vertically, extending into one or both nostrils
  • Cleft palate - a birth defect in which the roof of the mouth is split, extending from behind the teeth to the nasal cavity; often occurs with other birth defects such as cleft lip and partial deafness
  • Clinical trial - carefully monitored and planned testing of a new drug or treatment
  • Clitoris - a small female organ located near the opening of the vagina that swells when sexually aroused
  • Clone - an exact copy of a gene, cell, or organism
  • Closed fracture - a bone break that does not break the skin
  • Clotting factor - a substance in the blood that is needed for blood to harden and stop a wound from bleeding
  • Clubfoot - a genetic disorder in which the foot is twisted and misshapen
  • Cluster headache - severe pain that occurs suddenly and affects one side of the head, including the face and neck
  • Coagulation - a process that plays a large role in the hardening and thickening of blood to form a clot
  • Cocarcinogen - a substance that does not cause cancer by itself, but increases the effect of a substance that does cause cancer
  • Coccyx - four fused bones that form a triangular shape at the base of the spine (also known as the tailbone)
  • Cochlea - a coiled organ in the inner ear that plays a large role in hearing by picking up sound vibrations and transmitting them as electrical signals
  • Coitus - sexual intercourse
  • Cold sore - a small blister anywhere around the mouth that is caused by the herpes simplex virus
  • Colectomy - the complete or partial surgical removal of the large intestine (the colon), usually as treatment of a cancerous tumor or a narrowing and blockage of the intestine
  • Colic - waves of pain in the abdomen that increase in strength, disappear, and return; usually caused by a stone blocking a bile or urine passageway or an intestinal infection
  • Colitis - inflammation of the large intestine (the colon), which usually leads to abdominal pain, fever, and diarrhea with blood and mucus
  • Collapsed lung - a condition in which all or part of a lung cannot expand and fill with air
  • Colon - the main part of the large intestine, between the cecum and the rectum
  • Colonoscopy - investigation of the inside of the colon using a long, flexible fiberoptic tube
  • Color blindness - any vision disorder in which the person sees colors abnormally, has trouble distinguishing between them, or cannot see them at all
  • Colostomy - a surgical procedure in which some part of the colon is cut and moved to the surface of the abdomen so that feces can be passed into a bag worn outside of the body
  • Coma - a condition in which the area of the brain involved in maintaining consciousness is somehow affected, resulting in a state of unconsciousness in which the patient does not respond to stimulation
  • Comminuted fracture - a crushed or shattered bone
  • Common cold - an infection caused by a virus, which results in an inflamed lining of the nose and throat; characterized by a stuffy and runny nose and, sometimes, a sore throat
  • Communicable disease - a disease that can be passed from one individual to another
  • Compound fracture - a bone break that breaks the skin
  • Compression fracture - a break in a short bone in which its soft tissue is crushed
  • Computed tomography scanning - a technique for producing cross-sectional images of the body in which X-rays are passed through the body at different angles and analyzed by a computer; also called CT scanning or CAT scanning
  • Concussion - disturbance of electrical activity in the brain due to a blow to the head or neck, causing temporary loss of consciousness
  • Congenital - present or existing at the time of birth
  • Congestive heart failure - inability of the heart to efficiently pump blood through the body, causing buildup of blood in the veins and of other body fluids in tissue
  • Conjunctiva - the clear membrane covering the white of the eye and the inside of the eyelid that produces a fluid that lubricates the cornea and eyelid
  • Conjunctivitis - inflammation of the conjunctiva; commonly called pinkeye
  • Connective tissue - strong tissue that connects and supports body structures
  • Constipation - difficult or infrequent bowel movements of hard, dry feces
  • Contraindication - an aspect of a patient's condition that makes the use of a certain drug or therapy an unwise or dangerous decision
  • Contusion - damage to the skin and underlying tissue as a result of a blunt injury; a bruise
  • Corn - a thickened callus on the foot that is caused by an improperly fitting shoe
  • Cornea - the clear, dome-shaped front portion of the eye’s outer covering
  • Coronary arteries - the arteries that branch off from the aorta and supply oxygen-rich blood to the heart muscle
  • Coronary artery bypass surgery - an operation in which a piece of vein or artery is used to bypass a blockage in a coronary artery; performed to prevent myocardial infarction and relieve angina pectoris
  • Coronary heart disease - disorders that restrict the blood supply to the heart, including atherosclerosis
  • Coronary thrombosis - the blockage of a coronary artery by a blood clot
  • Coronary - describes structures that encircle another structure (such as the coronary arteries, which circle the heart); commonly used to refer to a coronary thrombosis or a heart attack
  • Corpuscle - a tiny, rounded structure in the body, such as a red or white blood cell
  • Corticosteroids - synthetic drugs that are used to replace natural hormones or to suppress the immune system and help prevent inflammation
  • Creatinine - a waste product that is filtered from the blood by the kidneys and expelled in urine
  • Croup - a usually mild and temporary condition common in children under the age of 4 in which the walls of the airways become inflamed and narrow, resulting in wheezing and coughing
  • Cruciate ligaments - two ligaments in the knee that cross each other and help stabilize the knee joint
  • Culture - the artificial growth of cells, tissue, or microorganisms such as bacteria in a laboratory
  • Curettage - the use of a sharp, spoonlike instrument (a curet) to scrape away tissue that is abnormal or to obtain a sample that can be analyzed
  • Cyanosis - a bluish discoloration of the skin, caused by low levels of oxygen in the blood
  • Cyst - a lump filled with either fluid or soft material, occurring in any organ or tissue; may occur for a number of reasons but is usually harmless unless its presence disrupts organ or tissue function
  • Cystectomy - surgical removal of the bladder; the bladder is often replaced with a short length of small intestine
  • Cystic fibrosis - an inherited disorder in which the lungs are prone to infection, and fats and other nutrients cannot be absorbed into the body
  • Cystoscopy - examination of the urethra and bladder using a long, thin, fiberoptic tube
  • Cystostomy - the surgical placement of a drainage opening in the bladder
  • D and C - see Dilatation and Curettage
  • DNA - deoxyribonucleic acid; responsible for passing genetic information in nearly all organisms
  • Debridement - surgical removal of dead, damaged, or infected tissue, or some foreign material from a wound or burn
  • Decompression sickness - the formation of gas bubbles in the body’s tissues as a result of a scuba diver ascending too quickly from depth; commonly called the bends
  • Deep-vein thrombosis - the formation of a blood clot inside of a deep-lying vein, usually in the legs
  • Defecation - the passing of feces out of the body through the anus; a bowel movement
  • Defibrillation - a short electric shock to the chest to normalize an irregular heartbeat
  • Degenerative arthritis - the breakdown of the cartilage lining the bones in joints, usually weight-bearing joints (such as the knee); causes stiffness and pain (also called osteoarthritis)
  • Dehydration - excessive, dangerous loss of water from the body
  • Dementia - a gradual decline in mental ability usually caused by a brain disease, such as
  • Depilatory - a chemical hair remover
  • Depot injection - injection of a drug into a muscle; the drug is designed to absorb slowly into the body
  • Depression - feelings of hopelessness, sadness, and a general disinterest in life, which for the most part have no cause and may be the result of a psychiatric illness
  • Dermabrasion - removal of the surface layer of skin with a sanding wheel to treat scarring or to remove tattoos
  • Dermatitis - inflammation of the skin
  • Dermis - the inner skin layer
  • Desensitization - the process of making a person less allergic to a substance by injecting gradually increasing amounts of the substance; sometimes done to prevent anaphylactic shock
  • Detoxification - treatment given either to fight a person's dependence on alcohol or other drugs or to rid the body of a poisonous substance and its effects
  • Dextrocardia - a rare genetic condition in which the heart is located on the right side of the body, instead of the left
  • Dextrose - another name for the sugar glucose
  • Diabetes insipidus - a rare condition characterized by increased urine production
  • Diabetes mellitus - a common form of diabetes in which the body cannot properly store or use glucose (sugar), the body's main source of energy
  • Dialysis - a procedure to treat kidney failure in which artificial means are used to filter waste, maintain acid-base balance, and remove excess fluid from the body
  • Diaper rash - a common condition in babies in which the skin in the diaper area becomes irritated and red, usually because of exposure to urine, feces, or heat
  • Diaphragm - the large, dome-shaped muscle separating the abdomen and chest that contracts and relaxes to make breathing possible; also, a thin, rubber dome that is used as a method of female contraception
  • Diastolic pressure - the blood pressure measured when the heart is at rest between beats
  • Diathermy - the use of high-frequency currents, microwaves, or ultrasound to produce heat in the body to increase blood flow, relieve pain, or destroy diseased tissue
  • Dilatation and Curettage - a procedure in which the vagina and cervix are widened and the lining of the uterus is scraped away to diagnose and treat disorders of the uterus
  • Diphtheria - a bacterial infection that causes a fever, headache, sore throat, and possibly death; diphtheria is rare in developed countries
  • Disk prolapse - a disorder in which one of the disks located between the vertebrae in the spine breaks down and the pulpy interior squeezes out, causing pressure on a nerve; commonly called a "slipped" or "ruptured" disk
  • Dislocation - displacement of the two bones in a joint
  • Distention - swelling, enlargement, or stretching
  • Diuretic - a drug that increases the amount of water in the urine, removing excess water from the body; used in treating high blood pressure and fluid retention
  • Diverticulitis - inflammation of diverticula (small sacs in the intestine's inner lining); can cause fever, pain, and tenderness
  • Dominant gene - a gene that always produces its effect when it is present
  • Dopamine - a chemical that transmits messages in the brain and plays a role in movement
  • Down syndrome - a genetic disorder in which a person’s cells have 1 too many chromosomes, causing moderate to severe mental handicap and a characteristic appearance
  • Duchenne muscular dystrophy - a genetic condition in boys in which nerves degenerate and muscles get progressively weaker
  • Duodenal ulcer - an erosion in the inner lining of the wall of the first part of the small intestine (called the duodenum)
  • Duodenum - the first part of the small intestine, immediately following the stomach
  • Dysentery - a severe intestinal infection, causing abdominal pain and diarrhea with blood or mucus
  • Dyspnea - difficulty breathing
  • Dystrophy - any disorder in which cells become damaged or do not develop properly because they do not receive adequate nutrition
  • ECG (sometimes called an EKG) - an electrocardiogram, which is a record of the electrical impulses that trigger the heartbeat; used to diagnose heart disorders
  • EEG - see Electroencephalography
  • Eardrum - a thin, oval-shaped membrane that separates the inner ear from the outer ear and is responsible for transmitting sound waves
  • Echocardiogram - an image of the heart that is created by high-frequency (ultrasound) sound waves
  • Eclampsia - a serious condition that occurs in late pregnancy, characterized by seizures in the woman
  • Ectopic - occurring at an abnormal position or time
  • Eczema - inflammation of the skin, usually causing itchiness and sometimes blisters and scaling; may be caused by allergies, but often occurs for no apparent reason
  • Edema - abnormal buildup of fluid in the body, which may cause visible swelling
  • Elective - describes a treatment or procedure that is not urgent and can be arranged at the patient’s convenience
  • Electroencephalography - a procedure for recording the electrical impulses of brain activity
  • Embolism - the blockage of a blood vessel by an embolus ]] - something previously circulating in the blood (such as a blood clot, gas bubble, tissue, bacteria, bone marrow, cholesterol, fat, etc)
  • Embryo - a term used to describe a child in the womb from fertilization to 8 weeks following fertilization
  • Emetic - a substance that causes vomiting; used to treat some cases of poisoning and drug overdose
  • Emphysema - a chronic disease in which the small air sacs in the lungs (the alveoli) become damaged; characterized by difficulty breathing
  • Encephalitis - inflammation of the brain, usually caused by a virus; may be very mild and barely noticeable, but is usually serious and can progress from headache and fever to hallucinations, paralysis, and sometimes coma
  • Endarterectomy - surgery performed to remove the lining of an artery that has been narrowed by fatty tissue buildup
  • Endemic - describes a disease that is always present in a certain population of people
  • Endocarditis - inflammation of the inner lining of the heart, usually the heart valves; typically caused by an infection
  • Endocardium - the inner lining of the heart
  • Endocrine gland - a gland that secretes hormones into the bloodstream
  • Endogenous - arising from inside of the body
  • Endometrial polyp - a growth (usually noncancerous) occurring on the lining of the uterus
  • Endometriosis - a condition in which fragments of the endometrium are found in other pelvic organs
  • Endometrium - the membrane that lines the uterus
  • Endophthalmitis - inflammation of the inside of the eye
  • Endorphin - a group of chemicals produced in the brain that reduce pain and positively affect mood
  • Endoscope - a lighted instrument used to view the inside of a body cavity
  • Endothelium - the layer of flat cells that lines the blood and lymph vessels, the heart, and other structures in the body
  • Endotracheal tube - a plastic tube that is fed down into the trachea through the mouth or nose to supply oxygen to a person who is not breathing properly
  • Enteritis - inflammation of the small intestine, usually causing diarrhea
  • Enterobiasis - infestation by a pinworm
  • Enuresis - the medical term for wetting the bed
  • Enzyme - a chemical, originating in a cell, that regulates reactions in the body
  • Epidemic - a term used to describe a disease that is rare then suddenly affects more people than usually expected
  • Epidermis - the outer layer of the skin
  • Epididymis - a long, coiled tube, exiting from the back of the testicle, in which sperm mature
  • Epidural anesthesia - a method of pain relief in which a painkilling drug is injected into the space surrounding the spinal cord to block sensations in the abdomen and lower body
  • Epilepsy - a disorder of the nervous system in which abnormal electrical activity in the brain causes seizures
  • Epinephrine - a hormone produced by the adrenal glands in response to stress, exercise, or fear; increases heart rate and opens airways to improve breathing; also called adrenaline
  • Episcleritis - a patch of inflammation on the outer layer of the white of the eye
  • Episiotomy - a surgical procedure in which an incision is made in the tissue between the vagina and anus to prevent tearing of this tissue during childbirth
  • Epithelium - the layer of cells that covers the body and lines many organs
  • Epstein-Barr virus - a virus that is the cause of mononucleosis and is involved in Burkitt’s lymphoma
  • Erysipelas - an infection caused by streptococci bacteria; characterized by fever and rash
  • Erythema - redness of the skin
  • Erythrocyte sedimentation rate - a measure of the time it takes for red blood cells to collect at the bottom of a sample of blood; an elevated rate may mean that there is inflammation somewhere in the body
  • Erythrocyte - a red blood cell
  • Erythroplakia - red patches in the mucous membranes of the mouth, throat, or voice box (larynx) that can become cancerous; risk factors include smoking pipes and chewing tobacco
  • Esophageal spasm - irregular contractions of the muscles in the esophagus, which lead to difficulty swallowing
  • Esophageal varices - swollen veins in the lower esophagus and possibly the upper part of the stomach; can cause vomiting of blood and passing of black stool
  • Esophagus - a tube-shaped canal in the digestive tract, connecting the throat to the stomach
  • Estrogen replacement therapy - treatment with synthetic estrogen drugs to relieve symptoms of menopause and to help protect women against osteoporosis and heart disease
  • Estrogen - a group of hormones (produced mainly in the ovaries) that are necessary for female sexual development and reproductive functioning
  • Eustachian tube - the tube that connects the middle ear and the back of the nose, draining the middle ear and regulating air pressure
  • Euthanasia - painlessly ending the life of a patient with an incurable disease who requests to die
  • Excision - the surgical removal of diseased tissue
  • Excretion - the process by which the body rids itself of waste
  • Exercise stress test - the monitoring of the heart during strenuous exercise, usually on a treadmill or exercise bicycle, to evaluate how the heart responds to stress
  • Exercise thallium test - an imaging test performed during and after an exercise stress test to evaluate functioning of the heart muscles
  • Exogenous - arising from outside of the body
  • Expectorant - a medication used to promote the coughing up of phlegm from the respiratory tract
  • Extensor muscle - a muscle that causes a joint or limb to straighten
  • External version - external repositioning of the fetus in the womb to the correct birth position
  • Extracorporeal shock wave lithotripsy - a procedure performed to destroy kidney stones using external shock waves
  • Extradural anesthesia - injection of an anesthetic into the space outside the dura mater, the fibrous membrane that envelops the spinal cord
  • FSH - see Follicle stimulating hormone
  • Facial palsy - inability to move the muscles of the face, usually on only one side, due to inflammation of a nerve
  • Failure to thrive - describes a baby who grows and gains weight slower than expected
  • Fallopian tube - either of two long, slender ducts connecting a woman's uterus to her ovaries, where eggs are transported from the ovaries to the uterus and sperm may fertilize an egg
  • Familial - a term describing a disorder or characteristic (such as male pattern baldness) that occurs within a family more often than would be expected
  • Fasciitis - inflammation of the layer of connective tissue that covers, separates, and supports muscles
  • Fatty acid - any of a number of carbon-, oxygen-, and hydrogen-containing molecules that make up fats
  • Febrile - a term used to describe something related to a fever, such as febrile seizures (seizures occurring in a child who has a fever)
  • Fecal occult blood test - a test that uses a piece of chemically sensitive paper to detect blood in a stool sample; used to screen for possible signs of cancer in the large intestine or rectum
  • Femoral artery - the main artery that supplies blood to the leg
  • Femur - the bone located between the hip and the knee; the thighbone
  • Fertility drug - a drug used to treat infertility that contains hormones or substances associated with hormones
  • Fertility - the ability to produce a child
  • Fertilization - the joining of an egg and a sperm, creating the first cell of a new life
  • Fetal alcohol syndrome - a combination of defects in a fetus as a result of the mother drinking alcohol during pregnancy
  • Fetal distress - physical distress experiencd by a fetus because of lack of oxygen
  • Fetal monitoring - the use of an instrument to record or listen to a fetus' heartbeat during pregnancy and labor
  • Fetal tissue transplant - an experimental procedure in which cells are taken from an aborted fetus and placed into the brain of a person with a brain disease such as Parkinson's
  • Fetus - the term used to refer to an unborn child from 8 weeks after fertilization to birth
  • Fiber - a constituent of plants that cannot be digested, which helps maintain healthy functioning of the bowels
  • Fiberoptics - thin, flexible instruments that transmit light and images, allowing structures inside of the body to be viewed
  • Fibrillation - rapid, inefficient contraction of muscle fibers of the heart caused by disruption of nerve impulses
  • Fibroadenoma - a noncancerous tumor commonly found in the breast
  • Fibrocystic breast disease - the most common cause of breast lumps
  • Fibroid - a noncancerous tumor of the uterus made up of smooth muscle and connective tissue
  • Fibroma - a noncancerous tumor of connective tissue
  • Fibrosis - abnormal formation of connective or scar tissue
  • Fifth disease - a childhood infection caused by a virus, which often starts as a rash on the cheeks and spreads
  • Fissure - a groove or slit on the body or in an organ
  • Fistula - an abnormal passageway from one organ to another or from an organ to the body surface
  • Fitness - a measure of a person's physical strength, flexibility, and endurance
  • Flatulence - excessive air or gas in the intestines, which is expelled through the anus
  • Floaters - small spots that float across the field of vision, caused by debris floating in the gel-like substance that fills the eye
  • Flu - see Influenza
  • Fluke - a parasitic flatworm that can infest humans
  • Fluoride - a mineral that helps protect teeth against decay
  • Fluoroscopy - a method used to view organ structure and function by passing X-rays through the body and monitoring the resulting image on a fluorescent screen
  • Folic acid - a vitamin essential to the production of red blood cells; plays an important role in the growth a developing fetus
  • Follicle stimulating hormone - a hormone produced by the pituitary gland in the brain that stimulates the testicles to produce sperm in males and causes eggs to mature in females
  • Follicle - a tiny pouchlike cavity in a structure of the body, such as a hair follicle
  • Folliculitis - the inflammation of hair follicles due to a bacterial infection, causing boils or tiny blisters containing pus
  • Fontanelles - the two soft spots on a baby’s scalp that are the result of gaps in the skull where bones have not yet fused
  • Food poisoning - stomach pain, diarrhea, and/or vomiting caused by eating contaminated food
  • Forceps delivery - the use of an instrument that cups the baby's head (called an obstetric forceps), to help deliver a baby
  • Forceps - instruments resembling tweezers that are used to handle objects or tissue during surgery
  • Foreign body - an object in an organ or body cavity that is not normally present
  • Foreskin - the loose skin that covers the head of the penis
  • Fracture - a bone break
  • Fraternal twins - twins that develop from two different eggs fertilized by two different sperm; are not identical
  • Free radical - see Oxygen free radical
  • Frostbite - damage to body tissue as a result of freezing
  • Fulminant - describes a disorder that begins suddenly and worsens quickly
  • Fungus - an organism that is dependent on another organism for nourishment
  • GI series - see Gastrointestinal series
  • GIFT - see Gamete intrafallopian transfer
  • Galactocele - a milk-filled tumor in a blocked breast milk duct
  • Galactorrhea - breast milk production by a woman who is not pregnant and has not just given birth
  • Galactose - a sugar that is formed from the breakdown of lactose
  • Galactosemia - a genetic disorder in which galactose cannot be converted into glucose
  • Gallbladder - a small, pear-shaped sac positioned under the liver, which concentrates and stores bile
  • Gallstone ileus - an abnormal condition in which a gallstone passes from the gallbladder into the intestines through an abnormal passage and blocks the intestine
  • Gallstone - a round, hard mass of cholesterol, bile, or calcium salts that is found in the gallbladder or a bile duct
  • Gamete intrafallopian transfer - a method of treating infertility in which eggs are taken from a woman's ovaries and fertilized with sperm and then the fertilized egg is injected into one of her fallopian tubes
  • Gamma globulin - a substance prepared from blood that carries antibodies to most common infections; also used in immunizations
  • Ganglion - a fluid-filled cyst attached to a tendon sheath or joint
  • Gangrene - death of a tissue because of a lack of blood supply
  • Gastrectomy - surgical removal of all or part of the stomach
  • Gastric acid - the digestive acid in the stomach
  • Gastric juice - digestive fluids produced by the lining of the stomach that break down proteins and destroy harmful organisms
  • Gastric lavage - washing out of the stomach with water, often to treat poisoning; commonly called "stomach pumping"
  • Gastric ulcer - a peptic ulcer
  • Gastrin - a hormone that stimulates the release of gastric acid in the stomach
  • Gastrinoma - a tumor that produces gastrin, making the stomach and duodenum more acidic
  • Gastritis - inflammation of the mucous membrane lining of the stomach; can have a number of causes, including viruses, bacteria, and use of alcohol and other drugs
  • Gastroenteritis - inflammation of the stomach and intestines
  • Gastrointestinal series - a set of X-rays, taken at different intervals after a barium sulfate solution is swallowed, to examine the gastrointestinal tract
  • Gastrointestinal tract - the part of the digestive system that includes the mouth, esophagus, stomach, and intestines
  • Gastroscopy - examination of the esophagus, stomach, and the first part of the small intestine (duodenum) using an endoscope inserted through the mouth
  • Gastrostomy - the surgical creation of an opening in the abdominal wall into the stomach for drainage or a feeding tube
  • Gaucher’s disease - a genetic disorder in which lipids cannot be properly broken down and build up in certain cells; causes enlargement of the spleen and liver, bone damage, and anemia
  • Gavage - an artificial feeding technique in which liquids are passed into the stomach by way of a tube inserted through the nose
  • Gene therapy - an experimental procedure in which disease-causing genes are replaced by normal, healthy genes
  • Gene - the basic unit of DNA, which is responsible for passing genetic information; each gene contains the instructions for the production of a certain protein
  • General anesthesia - a method of preventing pain in which the patient is induced to lose consciousness
  • Generic drug - a drug marketed under its chemical name, instead of a brand name
  • Genetic analysis - examination of DNA in a laboratory to diagnose genetic disorders
  • Genetic counseling - information and advice given to persons considering pregnancy about the risk that a child will have an inheritable birth defect or genetic disorder
  • Genetic disorder - a disorder caused partly or completely by a defect in genes, which carry hereditary information
  • Genetic engineering - the alteration of genetic information to change an organism; mainly used to produce vaccines and drugs such as insulin
  • Genital herpes - an infection caused by the herpes simplex virus, which causes a painful rash of fluid-filled blisters on the genitals; transmitted through sexual contact
  • Genital tract - the organs that make up the reproductive system
  • Genital wart - a growth on the skin in or around the vagina, penis, or anus, transmitted by sexual contact; can cause cancer of the cervix
  • Genome - the complete set of an organism’s genes
  • Geographic tongue - a condition in which the tongue is patchy where surface cells break down
  • Germ cell - a sperm or egg cell, or the immature form of either
  • German measles - the common name for Rubella
  • Gestation - the period of time between fertilization of an egg by a sperm and birth of a baby
  • Giardiasis - infection with a single-celled parasite, causing abdominal cramps, diarrhea, and nausea
  • Gingivectomy - surgical removal of a diseased part of the gums
  • Gingivitis - inflammation of the gums, typically caused by a buildup of plaque due to poor hygiene
  • Gland - a group of cells or an organ that produces substances (such as hormones and enzyme) that are used by the body
  • Glaucoma - a disease in which eye damage is caused by an increase in the pressure of the fluid within the eye
  • Glioblastoma multiforme - a fast-growing, cancerous brain tumor
  • Glioma - a brain tumor arising from cells that support nerve cells
  • Glomerulonephritis - inflammation of the filtering structures in the kidneys, hindering removal of waste products from the blood
  • Glomerulosclerosis - scarring of the filtering structures in the kidneys due to damage
  • Glossectomy - surgical removal of all or part of the tongue
  • Glucagon - a hormone produced by the pancreas that converts stored carbohydrates (glycogen) into glucose, the body’s energy source
  • Glucose tolerance test - a test that evaluates the body's response to glucose after a period of fasting; used to check for diabetes mellitus
  • Glucose - a sugar that is the main source of energy for the body
  • Glycogen - the main form that glucose, the body’s energy source, takes when it is stored
  • Glycosuria - glucose in the urine
  • Goiter - enlargement of the thyroid gland, which produces a swelling on the neck
  • Gonadotropic hormones - hormones that stimulate activity in the ovaries and testicles
  • Gonorrhea - a common sexually transmitted disease, characterized by painful urination or a discharge from the penis or vagina
  • Gout - a disorder marked by high levels of uric acid in the blood; usually experienced as arthritis in one joint
  • Graft - healthy tissue that is used to replace diseased or defective tissue
  • Grand mal - a type of seizure occurring with epilepsy, producing loss of consciousness and involuntary jerking movements
  • Granuloma - a mass of tissue that forms at a site of inflammation, injury, or infection as a part of the healing process
  • Graves' disease - an autoimmune disease that causes goiter, overproduction of thyroid hormones, and sometimes bulging eyeballs
  • Guillain-Barré syndrome - a peripheral nervous system disease in which nerve inflammation causes weakness, loss of movement, and loss of sensation in the arms and legs
  • Guthrie test - a blood test performed on babies to test for phenylketonuria
  • H1 (histamine) blocker - a drug that blocks the action of histamine; used to treat inflammation
  • H2 (histamine) blocker - a drug used in the treatment of peptic ulcers that blocks histamine from causing acid production in the stomach
  • HDL - see High-density lipoprotein
  • HIV - see Human immunodeficiency virus
  • HTLV - see Human T-cell lymphotrophic virus
  • Hair follicle - a tiny opening in the skin from which a hair grows
  • Halitosis - the clinical term for bad breath; commonly caused by poor oral hygiene or eating certain foods; if persistent it can be a sign of illness
  • Hallucination - a perception that occurs when there is actually nothing there to cause it (such as hearing voices when there are none)
  • Hammer toe - an abnormality in the tendons of the toe that causes the toe to be flexed at all times
  • Hamstring muscle - a muscle located at the back of the thigh that bends the leg at the knee and moves the leg backward
  • Hardening of the arteries - the common name for arteriosclerosis
  • Hashimoto’s disease - a disease in which the body’s immune system attacks cells of the thyroid gland, resulting in a decrease in thyroid hormones
  • Hay fever - the common name for allergic rhinitis
  • Heart attack - see Myocardial infarction
  • Heart block - a disorder of the heart caused by a blockage of the nerve impulses to the heart that regulate heartbeat; may lead to dizziness, fainting, or stroke
  • Heart disease - see Coronary heart disease
  • Heart failure - the inability of the heart to pump blood effectively
  • Heart rate - the rate at which the heart pumps blood, measured in the number of heartbeats per minute
  • Heart valve - the structure at each exit of the four chambers of the heart that allows blood to exit but not to flow back in
  • Heart-lung machine - a machine that takes over the functions of the heart and lungs during certain types of surgery
  • Heartburn - a burning sensation experienced in the center of the chest up to the throat; may be caused by overeating, eating spicy food, or drinking alcohol; recurrent heartburn may be caused by acid reflux
  • Heat exhaustion - fatigue, dizziness, and nausea experienced because of overexposure to heat; if not treated it can result in heat stroke
  • Heat stroke - a life-threatening condition resulting from extreme overexposure to heat, which disrupts the body's system of regulating temperature
  • Heel spur - an abnormal, often painful outgrowth of bone on the back of the heel
  • Heimlich maneuver - a first-aid technique for choking; dislodges an object that is blocking a person’s airway
  • Helper T cells - white blood cells, responsible for regulating other cells in the body's immune system, that are the main targets of the AIDS virus; also called CD4 cells
  • Hemangioma - a purple-red mark on the skin, caused by an excess of blood vessels
  • Hemarthrosis - bleeding into and swelling of a joint
  • Hematemesis - vomiting of blood
  • Hematocrit - the percentage of total blood volume that consists of red blood cells, which is determined by laboratory testing; can be an indicator of disease or injury
  • Hematoma - an accumulation of blood from a broken blood vessel
  • Hematuria - blood in the urine, which can be caused by urinary tract disorders (such as cysts, tumor, or stones) or by an infection
  • Hemochromatosis - a genetic disorder in which too much iron is absorbed from food
  • Hemodialysis - a method used to treat kidney failure, in which blood is passed through a machine that purifies it and returns it to the body
  • Hemoglobin - the pigment in red blood cells that is responsible for carrying oxygen; hemoglobin bound to oxygen gives blood its red color
  • Hemoglobinuria - hemoglobin in the urine
  • Hemolysis - the breakdown of red blood cells in the spleen, which is normal but can cause jaundice and anemia when the red blood cells are broken down too quickly
  • Hemophilia - an inherited disorder in which a person's blood lacks a certain protein important in forming blood clots, leading to excessive bleeding
  • Hemorrhage - the medical term for bleeding
  • Hemorrhoid - a bulging vein either at the opening of the anus or just inside the anus, often caused by childbirth or straining during bowel movements
  • Hemospermia - blood in the semen
  • Hemostasis - the stopping of bleeding by the body’s mechanisms
  • Hemothorax - an accumulation of blood between the chest wall and the lungs
  • Hepatectomy - surgical removal of all or part of the liver
  • Hepatic - a term used to describe something that is related to the liver
  • Hepatitis A - a form of hepatitis caused by the hepatitis A virus, usually transmitted by contact with contaminated food or water
  • Hepatitis B - a form of hepatitis (generally more serious than hepatitis A) caused by the hepatitis B virus, which is transmitted through sexual contact or contact with infected blood or body fluids
  • Hepatitis C - a form of hepatitis caused by the hepatitis C virus, which is transmitted through sexual contact or contact with infected blood or body fluids
  • Hepatitis D - a form of hepatitis that only causes symptoms when the individual is already infected with hepatitis B
  • Hepatitis - inflammation of the liver, which may be caused by a viral infection, poisons, or the use of alcohol or other drugs
  • Hepatoma - a cancerous tumor of the liver
  • Hepatomegaly - enlargement of the liver
  • Hereditary spherocytosis - a genetic disorder in which red blood cells are smaller, rounder, and more fragile than normal, causing hemolytic anemia
  • Hereditary - describes a genetic trait that is passed from parents to children
  • Hermaphroditism - a rare condition in which an individual is born with both male and female reproductive organs
  • Hernia - the bulging of an organ or tissue through a weakened area in the muscle wall
  • Herniated disk - see Disk prolapse
  • Herpes encephalitis - brain inflammation caused by a herpes simplex virus that has spread from another part of the body
  • Herpes simplex - infection by the herpes simplex virus, which causes blisterlike sores on the face, lips, mouth, or genitals; in rare cases, can also affect the eyes, fingers, or brain
  • Herpes zoster - see Shingles
  • Heterosexuality - being sexually attracted to members of the opposite sex
  • Hiatal hernia - a type of hernia in which the stomach bulges up into the chest cavity through an opening in the diaphragm
  • Hiccup - involuntary sudden contraction of the diaphragm along with the closing of the vocal cords, producing a "hiccup" sound
  • High-density lipoprotein - a type of protein found in the blood that removes cholesterol from tissues, protecting against heart disease
  • Hirschsprung's disease - a condition that is present at birth in which nerve cells do not develop in parts of the intestine, causing the intestine to narrow and block the passage of feces
  • Hirsutism - excessive hair or hair growth in unusual places, especially in women
  • Histamine - a chemical in some cells of the body that is released during allergic reactions, causing inflammation; also causes production of acid in the stomach and narrowing of the airways
  • Histoplasmosis - a respiratory disease acquired by inhaling the spores of a fungus found in soil, especially where there are bird or bat droppings
  • Hives - the common term for urticaria, an itchy, inflamed rash that results from an allergic reaction
  • Hodgkin's disease - a cancer of lymphoid tissue (found in lymph nodes and the spleen) that causes the lymph nodes to enlarge and function improperly; may cause illness, fever, loss of appetite, and weight loss
  • Homeostasis - the body's coordinated maintenance of the stable, internal environment by regulating blood pressure, blood sugar, body temperature, etc
  • Homocystinuria - a genetic disorder in which an enzyme deficiency causes a substance called homocystine to build up in the blood, leading to mental handicap and skeletal abnormalities
  • Homosexuality - being sexually attracted to members of the same sex
  • Hookworm - infestation by a small, round, blood-sucking parasite; commonly causes a rash on the foot, but can also cause cough, pneumonia, and anemia
  • Hormonal implant - surgical insertion of a small object just under the skin that slowly releases a synthetic hormone for purposes such as birth control
  • Hormone replacement therapy - the use of natural or artificial hormones to treat hormone deficiencies
  • Hormone - a chemical produced by a gland or tissue that is released into the bloodstream; controls body functions such as growth and sexual development
  • Hospice - a hospital or an area of a hospital dedicated to treating people who are dying, often of a specific cause
  • Hot flash - a sudden, temporary feeling of heat and sometimes sweating; usually occurs as a result of low estrogen levels in women because of menopause or after a hysterectomy
  • Human T-cell lymphotrophic virus - a virus similar to HIV that affects the same helper T cells, but usually accompanies adult T-cell leukemia or T-cell lymphomas
  • Human immunodeficiency virus - a retrovirus that attacks helper T cells of the immune system and causes acquired immunodeficiency syndrome (AIDS); transmitted through sexual intercourse or contact with infected blood
  • Hydramnios - an excess of amniotic fluid in the uterus during pregnancy
  • Hydrocele - a painless swelling of the scrotum, caused by a collection of fluid around the testicle; commonly occurs in middle aged men
  • Hydrocephalus - excess cerebrospinal fluid within the brain; commonly referred to as "water on the brain"
  • Hydrocortisone - a corticosteroid drug that is used to treat inflammation and allergies
  • Hygiene - the practice, maintenance, and study of health; commonly refers to cleanliness
  • Hymen - a thin fold of membrane partly closing the opening of the vagina; usually torn during first sexual intercourse or insertion of a tampon
  • Hyperactivity - a type of behavior characterized by excessive physical activity, sometimes associated with neurological or psychological causes
  • Hyperalimentation - a method of providing nutrients by the use of a tube or intravenously to a person who cannot eat food or needs nutrients because of an illness
  • Hyperbilirubinemia - a condition in which there is too much bilirubin, a substance produced when red blood cells are broken down; can lead to jaundice
  • Hypercalcemia - a condition marked by abnormally high levels of calcium in the blood; can lead to disturbance of cell function in the nerves and muscles and, if not treated, can be fatal
  • Hypercholesterolemia - an abnormally high level of cholesterol in the blood, which can be the result of an inherited disorder or a diet that is high in fat
  • Hyperglycemia - a condition characterized by abnormally high levels of glucose in the blood, usually as a result of untreated or improperly controlled diabetes mellitus
  • Hyperlipidemia - a general term for a group of disorders in which lipid levels in the blood are abnormally high, including hypercholesterolemia
  • Hyperparathyroidism - overactivity of the parathyroid glands, which increases calcium levels in the blood (called hypercalcemia) and decreases calcium in bones (causing osteoporosis)
  • Hyperplasia - the enlargement of an organ or tissue
  • Hypersensitivity - an excessive response of the body’s immune system to a foreign protein
  • Hypertension - abnormally high blood pressure, even when at rest
  • Hyperthermia - an abnormally high body temperature
  • Hyperthyroidism - overactivity of the thyroid gland, causing nervousness, weight loss, fatigue, and diarrhea
  • Hypertrophy - increase in the size of an organ due to an increase in the size of its cells
  • Hyperventilation - abnormally rapid breathing
  • Hypochondriasis - an abnormal condition in which a person is overly concerned with health and believes that he or she is suffering from a major illness despite medical opinion to the contrary
  • Hypodermic needle - a thin, hollow needle attached to a syringe; used to inject a medication under the skin, into a vein, or into a muscle
  • Hypoglycemia - abnormally low levels of glucose in the blood
  • Hypoplasia - failure of a tissue or organ to develop normally
  • Hypotension - the medical term for abnormally low blood pressure, which results in reduced blood flow to the brain, causing dizziness and fainting
  • Hypothermia - an abnormally low body temperature
  • Hypothyroidism - underactivity of the thyroid gland, causing tiredness, cramps, a slowed heart rate, and possibly weight gain
  • Hypoventilation - a slower-than-normal breathing rate
  • Hypoxemia - a reduced level of oxygen in the blood
  • Hypoxia - a reduced level of oxygen in tissues
  • Hysterectomy - surgical removal of the uterus
  • Hysteria - a term used to describe symptoms that are caused by mental stress and occur in someone who does not have a mental disorder
  • Hysterosalpingography - an X-ray examination performed to examine the inside of the uterus and fallopian tubes, in order to investigate and possibly treat infertility
  • Hysteroscopy - a method used to examine the inside of the uterus and the cervix using a viewing instrument
  • IQ - intelligence quotient; a measure of a person's intelligence as determined by specific tests
  • IUD - see Intrauterine device
  • IVF - see In vitro fertilization
  • Iatrogenic - a term used to describe a disease, disorder, or medical condition that is a direct result of medical treatment
  • Ichthyosis - a variety of diseases in which the skin is dry and scaly
  • Idiopathic - a term used to describe something that occurs of an unknown cause
  • Ileostomy - a surgical procedure in which the lower part of the small intestine (the ileum) is cut and brought to an opening in the abdominal wall, where feces can be passed out of the body
  • Ileum - the lowest section of the small intestine, which attaches to the large intestine
  • Ilium - one of the two bones that form the hip on either side of the body
  • Imaging - the technique of creating pictures of structures inside of the body using X-rays, ultrasound waves, or magnetic fields
  • Immune deficiency - impairment of the immune system, which reduces protection against infection and illness
  • Immune system - the cells, substances, and structures in the body that protect against infection and illness
  • Immunity - resistance to a specific disease because of the responses of the immune system
  • Immunization - the process of causing immunity by injecting antibodies or provoking the body to make its own antibodies against a certain microorganism
  • Immunocompromised - weakening of the body’s immune system
  • Immunodeficiency - failure of the body’s immune system to fight disease
  • Immunoglobin - proteins in blood and tissue fluids that help destroy microorganisms such as bacteria and viruses
  • Immunology - the study of the immune system, including how it functions and disorders that affect it
  • Immunostimulant - a drug that increases the ability of the body’s immune system to fight disease
  • Immunosuppressant - a drug that inhibits the activity of the immune system; used to prevent rejection of a transplant organ and in disorders where the body's immune system attacks its own tissues
  • Impacted fracture - a bone break in which the two broken ends have been forced into each other
  • Imperforate anus - a birth defect in which the opening of the anus is not formed normally
  • Impetigo - a highly contagious skin infection caused by bacteria, usually occurring around the nose and mouth; commonly occurring in children
  • Implant - an organ, tissue, or device surgically inserted and left in the body
  • Impotence - the inability to acquire or maintain an erection of the penis
  • In situ - "in place"; often describes a cancer that has not spread
  • In vitro fertilization - a treatment for infertility in which an egg and a sperm are joined outside the woman's body, and the fertilized egg is then inserted into the uterus or fallopian tube
  • In vitro - "in glass"; a biological test or process that is carried out in a laboratory
  • In vivo - "in the living body"; a biological process that occurs inside of the body
  • Incompetent cervix - an abnormally weak cervix, which widens prematurely during pregnancy as a result of the weight of a developing fetus; may result in a miscarriage
  • Incontinence - inability to hold urine or feces inside of the body
  • Incubation period - the time period between when an infectious organism enters the body and when symptoms occur
  • Indigestion - uncomfortable symptoms brought on by overeating or eating spicy, rich, or fatty foods; characterized by heartburn, pain in the abdomen, nausea, and gas, and can be more serious if recurrent
  • Induction of labor - the use of artificial means to start the process of childbirth
  • Infarction - tissue death due to lack of blood supply
  • Infection - disease-causing microorganisms that enter the body, multiply, and damage cells or release toxins
  • Infective arthritis - arthritis caused by bacteria from a wound or the bloodstream entering a joint
  • Infertility - the inability to have children as a result of sexual intercourse
  • Inflammation - redness, pain, and swelling in an injured or infected tissue produced as a result of the body's healing response
  • Inflammatory bowel disease - the general term for two inflammatory disorders affecting the intestines; also known as Crohn's disease and ulcerative colitis
  • Inflammatory joint disease - any type of arthritis that causes a joint to become inflamed
  • Influenza - a viral infection characterized by headaches, muscle aches, fever, weakness, and cough; commonly called the "flu"
  • Informed consent - agreement to undergo a medical procedure after the technique, its risks, and its possible complications have been explained
  • Infusion - the introduction of a substance, such as a drug or nutrient, into the bloodstream or a body cavity
  • Ingestion - taking something into the body through the mouth
  • Ingrown toenail - a painful condition of the big toe in which the nail grows into the skin on either side, causing inflammation and/or infection
  • Inguinal hernia - the bulging of a portion of the intestines or abdominal tissue into the muscles of the groin (the area just below the abdomen)
  • Inhaler - a device used to introduce a powdered or misted drug into the lungs through the mouth, usually to treat respiratory disorders such as asthma
  • Inheritance - the passing of traits from parent to child through genes
  • Injection - the use of a syringe and needle to insert a drug into a vein, muscle, or joint or under the skin
  • Insemination - the placement of semen into a woman's uterus, cervix, or vagina
  • Insomnia - difficulty falling or remaining asleep
  • Insulin - a hormone made in the pancreas that plays an important role in the absorption of glucose (the body's main source of energy) into muscle cells
  • Insulinoma - a noncancerous tumor of the insulin-producing cells of the pancreas; the tumor releases excess insulin into the blood, causing glucose levels to drop dangerously low
  • Intensive care - close monitoring of a patient who is seriously ill
  • Interferon - a protein produced by body cells that fights viral infections and certain cancers
  • Internal fixation - a method of holding a broken bone in place using surgically inserted screws, rods, or plates
  • Interstitial cystitis - persistent inflammation of the lining and muscle of the bladder
  • Interstitial lung disease - a disease of the connective tissue surrounding the air sacs of the lungs that causes a dry cough, scarring of lung tissue, and shortness of breath
  • Interstitial pulmonary fibrosis - scarring of connective tissue in the lungs that leads to shortness of breath
  • Interstitial radiation therapy - a treatment for cancer in which a radioactive material is inserted into or near a tumor to provide direct radiation
  • Interstitial - lying between body structures or in the interspaces of tissues
  • Intervertebral disks - broad, flat cartilage structures containing a gel-like fluid that cushion and separate vertebrae
  • Intestinal bypass - a surgical procedure in which the beginning of the large intestine is joined to its end so that less food is absorbed; because of serious side effects, usually performed only on seriously obese people
  • Intestine - a long, tube-shaped organ that extends from the stomach to the anus; absorbs food and water and passes the waste products of digestion as feces
  • Intra-aortic balloon pump - a small balloon inserted into the aorta that helps to circulate blood by inflating between heartbeats
  • Intractable - describes a condition that does not respond to treatment
  • Intramedullary rod - a strong metal rod that is placed inside of a broken bone to help it heal correctly
  • Intraocular pressure - the pressure of the fluids within the eye
  • Intrauterine device - a device inserted into the uterus that helps to prevent pregnancy
  • Intravenous - inside of or into a vein
  • Intrinsic - a term used to describe something originating from or located in a tissue or organ
  • Intubation - the passage of a tube into an organ or body structure; commonly used to refer to the passage of a tube down the windpipe for artificial respiration
  • Invasive - describes something that spreads throughout body tissues, such as a tumor or microorganism; also describes a medical procedure in which body tissues are penetrated
  • Involuntary - occurring without a person’s control or participation
  • Iodine - an element for the formation of thyroid hormones
  • Ionizing radiation - radiation that damages cells or genes; can be used to treat cancer
  • Iris - the colored part of the eye
  • Iron-deficiency anemia - a type of anemia caused by a greater-than-normal loss of iron due to bleeding, problems absorbing iron, or a lack of iron in the diet
  • Iron - a mineral necessary for the formation of important biological substances such as hemoglobin, myoglobin, and certain enzymes
  • Irrigation - the cleansing of a wound by flushing it with water, a medicated solution, or some other fluid
  • Irritable bladder - involuntary contractions of muscles in the bladder, which can cause lack of control of urination
  • Irritable bowel syndrome - abnormal muscle movement in the intestines, which causes abdominal pain and irregular bowel movements (diarrhea, constipation, or both)
  • Ischemia - a condition in which a tissue or organ does not receive a sufficient supply of blood
  • Jaundice - yellowing of the skin and whites of the eyes because of the presence of excess bilirubin in the blood; usually a sign of a disorder of the liver
  • Jock itch - an infection in the groin area caused by a fungus
  • Juvenile rheumatoid arthritis - a rare form of persistent joint inflammation that affects children
  • Kaposi's sarcoma - a skin cancer that is characterized by purple-red tumors that start at the feet and spread upward on the body; commonly occurs in people who have AIDS
  • Kawasaki disease - a childhood disease causing fever, rash, skin peeling, swollen lymph nodes, and possibly complications of the heart and brain
  • Keloid - a raised, firm, thick scar that forms as a result of a defect in the natural healing process
  • Keratin - a tough protein found in skin, nails, and hair
  • Keratitis - inflammation of the cornea
  • Keratolytic - drugs that remove the keratin-containing outer layer of skin; used to treat skin disorders such as warts and dandruff
  • Keratoplasty - surgical replacement or reshaping of the cornea
  • Keratosis - a growth on the skin that is the result of overproduction of the protein keratin
  • Ketoacidosis - the dangerous accumulation of chemicals called ketones in the blood, sometimes occurring as a complication of diabetes mellitus; also called ketosis
  • Kidney stone - a hard mass composed of substances from the urine that form in the kidneys
  • Kidney - one of two organs that are part of the urinary tract; responsible for filtering the blood and removing waste products and excess water as urine
  • Killer T cells - white blood cells that are part of the immune system and destroy microorganisms and cancer cells
  • Kilocalorie - a unit of energy; equal to a nutritional calorie
  • Kimmelstiel-Wilson syndrome - a kidney disorder that can occur as a complication of diabetes mellitus; can cause swelling, high blood pressure, and kidney failure
  • Klinefelter’s syndrome - a genetic disorder in which a man has at least 1 extra X chromosome in his cells, causing infertility and female characteristics
  • Knee-jerk reflex - a test for a reflexive extension of the leg to check the functioning of the nervous system; tapping the knee just below the kneecap should cause the lower part of the leg to jerk upward
  • Kyphosis - excessive curvature of the spine, which usually affects the top part of the spine and causes a hump
  • LDL - see Low-density lipoprotein
  • LH - see Luteinizing hormone
  • Labia - the two pairs of skinfolds that protect the opening of the vagina
  • Labor - the interval from onset of contractions to birth of a baby
  • Labyrinthitis - inflammation of the fluid-containing chamber of the inner ear (called the labyrinth) that maintains balance; can cause a feeling that one's surroundings are spinning around (known as vertigo)
  • Laceration - a torn or ragged wound
  • Lactase deficiency - an inherited disorder in which a person does not have the enzyme lactase, which breaks down lactose (the sugar found in dairy products); lactase deficiency leads to lactose intolerance, which means the inability to digest lactose
  • Lactation suppression - a decrease in milk production during pregnancy as a result of high levels of estrogen in the blood
  • Lactation - the production of breast milk after giving birth
  • Lactic acid - an acid produced by glucose-burning cells when these cells have an insufficient supply of oxygen
  • Lactose intolerance - inability to break down and absorb the sugar lactose
  • Lactose - the sugar found in dairy products
  • Lamaze method - a method of preparing for childbirth that stresses physical conditioning, relaxation, and breathing exercises
  • Laminectomy - a surgical procedure that removes part of a vertebra to relieve pressure on the spinal cord or a nerve branching from the spinal cord
  • Laparoscope - a viewing instrument used to examine and treat disorders in the abdominal cavity; consists of a long tube with an eyepiece, a lens, and often a camera, which allows the image to be viewed on a monitor
  • Laparoscopic cholecystectomy - surgical removal of the gallbladder using a laparoscope
  • Laparoscopy - a procedure done to examine the abdominal cavity using a laparoscope, usually to investigate pelvic pain or gynecologic conditions such as infertility
  • Large intestine - the part of the digestive tract that is located between the small intestine and the anus
  • Large-cell carcinoma - one of the 4 major types of lung cancer
  • Laryngectomy - surgical removal of all or part of the voice box (larynx) as a treatment for cancer
  • Laryngitis - inflammation of the voice box, usually caused by a viral infection; characterized by a hoarse voice
  • Larynx - the medical term for the voice box, the organ in the throat that produces voice and also prevents food from entering the airway
  • Laser treatment - the use of a laser (a concentrated beam of light) to perform medical procedures, such as the destruction of tumors
  • Latent infection - an infection that lies dormant in the body for months or years but can reappear
  • Lateral - on one side
  • Laxatives - drugs used to clear feces from the intestines; commonly used to treat constipation
  • Lazy eye - the common name for the visual defect resulting from untreated strabismus, in which the eyes are not correctly aligned
  • Lead poisoning - damage to the brain, nerves, red blood cells, or digestive system because of ingestion of lead
  • Learning disability - any of a variety of disorders, including hyperactivity, dyslexia, and hearing problems, that can interfere with a person's ability to learn
  • Legionnaires’ disease - a form of pneumonia that is mainly spread through airconditioning systems and water
  • Leiomyoma - a noncancerous tumor of smooth muscle
  • Leishmaniasis - a group of parasitic diseases affecting the skin, mucous membranes, and internal organs; transmitted by the bite of a sandfly
  • Leptospirosis - infection by a spiral-shaped bacterium that affects the skin, eyes, muscles, kidneys, and liver; leptospirosis is carried by rodents
  • Lesch-Nyhan syndrome - a genetic disorder affecting only men that causes mental handicap, self-mutilation, and aggressive behavior
  • Lesion - an abnormality of structure or function in the body
  • Leukemia - a group of bone marrow cancers in which white blood cells divide uncontrollably, affecting the production of normal white blood cells, red blood cells, and platelets
  • Leukocyte count - the number of white blood cells in the blood, which is used as a measure of health and possible infection
  • Leukocyte - another name for a white blood cells
  • Leukodystrophy - a group of childhood genetic disorders in which the protective coverings of the nerves are destroyed
  • Leukoplakia - white patches that can develop in the mouth or on the penis or the opening of the vagina and are potentially cancerous
  • Lichen planus - a common skin disease in which itchy, small, pink or purple spots appear on the arms or legs
  • Ligament - a tough, elastic band of tissue that connects bones and suupports organs
  • Ligation - the process of closing a blood vessel or duct by tying it off
  • Lipid-lowering drugs - drugs taken to lower the levels of specific fats called lipids in the blood in order to reduce the risk of narrowing of the arteries
  • Lipidosis - any disorder in which fats cannot be properly broken down by the digestive system
  • Lipids - a group of fats stored in the body and used for energy
  • Lipoma - a noncancerous tumor of fatty tissue
  • Lipoproteins - substances containing lipids and proteins, comprising most fats in the blood
  • Liposarcoma - a cancerous tumor of fatty tissue
  • Liposuction - a surgical procedure in which fat is removed from areas of the body using a suction pump
  • Listeriosis - a rare bacterial infection acquired by eating undercooked infected meat or from infected live animals; can be dangerous to newborns and the elderly
  • Lithotripsy - a procedure done to break up stones in the urinary tract using ultrasonic shock waves, so that the fragments can be easily passed from the body
  • Liver failure - the final stage of liver disease, in which liver function becomes so impaired that other areas of the body are affected, most commonly the brain
  • Liver - the largest organ in the body, producing many essential chemicals and regulating the levels of most vital substances in the blood
  • Lobe - a well-defined, separate part of an organ
  • Lobectomy - surgical removal of a lobe
  • Local anesthesia - a method of preventing pain by inducing the loss of sensation in a certain area of the body while the patient remains awake
  • Locked joint - a joint that cannot be moved because of a disease or a lodged piece of bone or cartilage
  • Lockjaw - a spasm of the jaw muscles that prevents the mouth from opening, such as that caused by tetanus
  • Locomotor system - the structures of the body that are responsible for its movement
  • Lordosis - the inward curvature of the spine at the lower back, which is normal to a certain degree; abnormal as a result of certain medical conditions, being overweight, or having muscle problems
  • Lou Gehrig's disease - see Amyotrophic lateral sclerosis
  • Low-density lipoprotein - a type of lipoprotein that is the major carrier of cholesterol in the blood, with high levels associated with narrowing of the arteries and heart disease
  • Lumbago - dull, aching pain in the lower back
  • Lumbar puncture - a procedure in which a needle is inserted into the lower region of the spinal canal to take out a sample of spinal fluid or to inject a drug
  • Lumbar spine - the lower part of the spine between the lowest pair of ribs and the pelvis; made up of five vertebrae
  • Lumpectomy - surgical removal of a section of breast containing cancer
  • Lung collapse - a condition in which all or part of a lung cannot expand and fill with air
  • Lungs - two organs in the chest that take in oxygen from the air and release carbon dioxide
  • Lupus erythematosus - a disorder of the immune system that causes inflammation of connective tissue
  • Luteinizing hormone - a hormone produced by the pituitary gland that causes the ovaries and testicles to release sex hormones and plays a role in the development of eggs and sperm
  • Lyme disease - a disease caused by bacteria transmitted through the bite of a tick; characterized by fever, rash, and inflammation of the heart and joints
  • Lymph node - a small gland that is part of the immune system; contains white blood cells and antibodies and helps fight against the spread of infection
  • Lymph - a milky fluid containing white blood cells, proteins, and fats; plays an important role in absorbing fats from the intestine and in the functioning of the immune system
  • Lymphadenopathy - swollen lymph nodes
  • Lymphangiography - an X-ray procedure that creates images of the lymphatic system
  • Lymphatic system - a network of vessels that drain lymph back into the blood
  • Lymphocyte - a white blood cell that is an important part of the body's immune system, helping to destroy invading microorganisms
  • Lymphocytic leukemia - a disease in which white blood cells called lymphocytes divide uncontrollably
  • Lymphogranuloma venereum - a sexually transmitted chlamydial infection; common in countries with a tropical climate
  • Lymphomas - a group of cancer of the lymph nodes and spleen that can spread to other parts of the body
  • Lymphosarcoma - another name for a non-Hodgkin's sarcoma; a cancerous tumor in lymphoid tissue
  • MAO inhibitor - see Monoamine oxidase inhibitor antidepressant
  • MRI - see Magnetic resonance imaging
  • MS - see Multiple sclerosis
  • Macula - the area of the retina that allows fine details to be observed at the center of vision; also refers to any small, flat spot on the skin
  • Macular degeneration - gradual loss of vision due to deterioration of nerve tissue in the retina
  • Magnesium - a mineral that is essential for many body functions, including nerve impulse transmission, formation of bones and teeth, and muscle contraction
  • Magnetic resonance imaging (MRI) - a technique that uses magnetic fields and radio waves to create high-quality cross-sectional images of the body without using radiation
  • Malabsorption - an impaired ability of the lining of the small intestine to absorb nutrients from food
  • Malaria - a parasitic disease spread by mosquitos that causes chills and fever; potentially fatal complications in the liver, kidneys, blood, and brain are possible
  • Malformation - abnormal development of an organ or tissue
  • Malignant hyperthermia - a reaction to certain anesthesia gases involving intense muscle contractions and a high fever
  • Malignant melanoma - the most serious type of skin cancer, in which a mole changes shape, darkens, becomes painful, and/or bleeds easily
  • Malignant - a word used to describe a condition that is characterized by uncontrolled growth and/or that can be fatal, such as a cancerous tumor
  • Mallory-Weiss syndrome - a condition associated with alcoholism in which the lower end of the esophagus tears, causing vomiting of blood
  • Mammography - an X-ray procedure done to detect breast cancer
  • Mammoplasty - a general term for a cosmetic operation on the breasts; includes breast reduction, enlargement, and reconstruction after a mastectomy
  • Mandible - another term for the lower jaw
  • Mania - a mental disorder characterized by extreme excitement, happiness, overactivity, and agitation; usually refers to the high of the highs and lows experienced in manicdepressive disorder
  • Manic-depressive disorder - a mental disorder characterized by extreme mood swings, including either mania, depression, or a continuing shift between the two extremes
  • Marfan's syndrome - a rare genetic disorder that affects connective tissue, leading to abnormalities of joints, bones, tendons, ligaments, arteries, and/or the heart
  • Mast cell - a type of cell present in most body tissues that releases substances in response to an allergen, which causes symptoms such as inflammation
  • Mastectomy - a surgical procedure in which all or part of the breast is removed to prevent the spread of cancer
  • Mastitis - inflammation of the breast, which is usually caused by a bacterial infection
  • Maxilla - one of two bones that form the upper jaw, the roof of the mouth, and the center portion of the face
  • Measles - an illness caused by a viral infection, causing a characteristic rash and a fever; primarily affects children
  • Meconium - thick, sticky, greenish-brown stool passed by a postmature fetus, or one experiencing fetal distress, into the amniotic fluid, or by an infant during the first couple of days after birth
  • Medial - a term used to describe something situated on or near the midline of the body or a body structure
  • Median nerve - a nerve running down the arm to the hand; controls muscle movement in the forearm and hand and conveys sensation from part of the hand
  • Mediastinoscopy - investigation of the central chest compartment using an endoscope that is inserted through an incision in the neck
  • Medulla - the center part of an organ or body structure; sometimes used to refer to the lower part of the brain stem
  • Medulloblastoma - a type of cancerous tumor, occurring in the section of the brain that controls posture and balance; found mainly in children
  • Megacolon - a severely swollen large intestine, causing severe constipation and abdominal bloating; may be present at birth or develops later
  • Megaloblastic anemia - a type of anemia in which a lack of the vitamin B12 or folic acid interferes with red blood cells and causes them to be enlarged and deformed, resulting in tiredness and weight loss
  • Meiosis - the type of cell division that occurs only in the ovaries and testicles, producing cells with half the genes of the original cell; these cells then form eggs and sperm
  • Melanin - the pigment that gives skin, hair, and eyes their coloring
  • Melanocyte-stimulating hormone - a hormone that coordinates pigmentation of the skin, eyes, and hair
  • Melanocytes - cells that produce the pigment melanin
  • Melanoma - a skin tumor composed of cells called melanocytes
  • Menarche - the beginning of menstruation
  • Meniere's disease - a disorder of the inner ear, causing hearing loss, ringing in the ear, and the sensation that one's surroundings are spinning
  • Meninges - the three membranes that surround and protect the spinal cord and brain
  • Meningioma - a rare noncancerous tumor developing in the protective membranes covering the brain called the meninges; can cause headaches and problems with vision and mental function
  • Meningitis - inflammation of the meninges; usually caused by infection by a microorganism (meningitis caused by bacteria is life-threatening; viral meningitis is milder)
  • Meningocele - a protrusion of the meninges through an opening in the skull or spinal cord due to a genetic defect
  • Meniscectomy - surgical removal of all or part of a cartilage disk from a joint
  • Meniscus - a crescent-shaped pad of cartilage in joints that helps to reduce friction
  • Menopause - the period in a woman's life when menstruation stops, resulting in a reduced production of estrogen and cessation of egg production
  • Menorrhagia - excessive loss of blood during menstruation, which can be caused by disorders of the uterus
  • Menstrual cycle - the periodic discharge of blood and mucosal tissue from the uterus, occurring from puberty to menopause in a woman who is not pregnant
  • Menstruation - the shedding of the lining of the uterus during the menstrual cycle
  • Mesenteric infarction - death of tissue in the intestine due to lack of blood supply to that tissue
  • Mesenteric lymphadenitis - inflammation of lymph nodes in an abdominal membrane
  • Mesothelioma - a cancerous tumor occurring in the lining of the lungs and chest cavity, often associated with exposure to asbestos dust
  • Mesothelium - a tissue layer that lines the heart, abdomen, chest cavity, and lungs
  • Messenger RNA - an RNA molecule that transports the information stored in DNA out of a cell's nucleus in order to make proteins
  • Metabolic rate - the speed at which the body uses energy
  • Metabolism - a general term for all of the chemical processes that occur in the body
  • Metabolite - any substance that takes part in a chemical reaction in the body
  • Metastasis - the spreading of a cancerous tumor to another part of the body through lymph, blood, or across a cavity; also sometimes refers to a tumor that has been produced in this way
  • Metered-dose inhaler - an inhaler that gives a specific amount of medication with each use
  • Microbe - another term for a microorganism, especially one that causes disease
  • Microbiology - the study of microorganisms
  • Microcephaly - an abnormally small head
  • Microdiskectomy - surgical removal of the protruding part of a prolapsed disk
  • Microorganism - any tiny, single-celled organism (such as a bacterium, virus, or fungus)
  • Microsurgery - a surgical technique that uses a special binocular microscope to operate on tiny, delicate, or hard-to-reach tissues
  • Micturition syncope - fainting or feeling weak while standing at the toilet; caused by an abnormal heartbeat or a drop in blood pressure
  • Middle ear effusion - the buildup of fluid in the middle ear, which can affect hearing
  • Middle ear - the small cavity between the eardrum and inner ear; contains three tiny, linked bones that transmit sound to the inner ear
  • Midwifery - a profession concerned with providing care to a mother and baby during pregnancy and childbirth
  • Migraine - a severe headache, usually accompanied by vision problems and/or nausea and vomiting, and that typically recurs
  • Mineral - a substance that is a necessary part of a healthy diet (such as potassium, calcium, sodium, phosphorus, and magnesium)
  • Minipill - an oral contraceptive containing only the synthetic hormone progesterone (birth control pills contain estrogen and progesterone)
  • Miotic - a drug that causes the pupil to constrict
  • Miscarriage - expulsion of a fetus before it has developed sufficiently to survive on its own
  • Mites - small eight-legged animals, many of which burrow and feed on blood
  • Mitosis - the process by which most cells divide in order to reproduce
  • Mitral insufficiency - a problem with the ability of the mitral valve in the heart to close, which causes the heart to pump harder and reduces its efficiency
  • Mitral stenosis - a condition in which the mitral valve in the heart becomes narrowed, making the heart work harder to pump blood; can lead to symptoms such as shortness of breath
  • Mitral valve prolapse - a common condition in which the mitral valve in the heart is deformed, causing blood to leak back across the valve; characterized by a heart murmur and sometimes chest pain and disturbed heart rhythm
  • Mitral valve - the valve in the heart that allows blood to flow from the left atrium to the left ventricle, but prevents blood from flowing back in
  • Modified radical mastectomy - a treatment for breast cancer in which the entire breast, a section of the chest muscle, and lymph nodes in the chest and underarm are removed
  • Molar tooth - large, strong teeth at the back of the jaw, primarily used to grind food
  • Mole - a brown to dark-brown spot on the skin that can be flat or raised
  • Molecule - the smallest unit of a substance that possesses its characteristics
  • Molluscum contagiosum - a viral infection that causes white bumps on the skin; usually clears up in a few months
  • Mongolian spot - a brown to blue-black spot on the lower back and buttocks at birth, caused by a concentration of pigment-producing cells; usually disappears by the age of 3 or 4 years
  • Monoamine oxidase inhibitor antidepressant - a substance that works by stopping an enzyme that breaks down stimulating chemicals in the brain; used to treat depression
  • Monoclonal antibodies - an antibody that is produced in the laboratory so that it will react with only one specific foreign protein; used to help diagnose certain kinds of cancer
  • Mononucleosis - an infection caused by a virus that invades a type of white blood cell called a monocyte, causing fever, sore throat, and swollen lymph nodes
  • Monounsaturated fat - a type of fat that is thought to be beneficial in the prevention of coronary heart disease; found in foods such as olive oil and peanut oil
  • Morbidity - the state of being ill or having a disease
  • Morning sickness - nausea and vomiting experienced early in a pregnancy, affecting about half of all pregnant women
  • Mortality - the death rate, measured as the number of deaths per a certain population; may describe the population as a whole, or a specific group within a population (such as infant mortality)
  • Motor nerve - a nerve that carries messages to a muscle that cause the muscle to contract
  • Motor neuron disease - degeneration of the nerves in the spinal cord and brain that are responsible for muscle movement, causing weakness and muscle deterioration
  • Mouth-to-mouth resuscitation - a method of artificial breathing in which someone rhythmically forces air into the lungs of a person who has stopped breathing
  • Mucocele - a sac or body cavity that is swollen because of the production of mucus by the cells in its lining
  • Mucolytic - a drug that lessens the sticky quality of phlegm and makes it easier to cough up
  • Mucous membrane - the soft, pink layer of cells that produce mucus in order to keep body structures lubricated; found in structures such as the eyelids, respiratory tract, and urinary tract
  • Mucus - a slippery fluid produced by mucous membranes that lubricates and protects the internal surfaces of the body
  • Multi-infarct dementia - dementia caused by multiple strokes
  • Multiple myeloma - a cancer that causes uncontrolled production of white blood cells in the bone marrow
  • Multiple pregnancy - the presence of more than one fetus in the uterus, such as occurs with twins
  • Multiple sclerosis - a disease in which the protective coverings (myelin) of nerve fibers in the brain are gradually destroyed; symptoms vary from numbness to paralysis and loss of control of bodily function
  • Multiple-gated acquisition scan - a technique for evaluating heart efficiency by measuring blood flow into and out of the heart
  • Mumps - a viral infection that causes inflammation of salivary glands; primarily affects children
  • Murmur - a characteristic sound (heard through a stethoscope) of blood flowing irregularly through the heart; can be harmless or may be an indication of disease
  • Muscle fibers - specialized, contracting cells that are bundled together to form muscles
  • Muscle relaxants - a group of drugs used to relieve muscle spasm and to treat conditions such as arthritis, back pain, and nervous system disorders such as stroke and cerebral palsy
  • Muscle tone - the natural tension in resting muscles
  • Muscle wasting - the degeneration of a muscle (loss of bulk), caused by disease or starvation
  • Muscular dystrophy - a rare genetic disorder in which muscles degenerate gradually and strength is lost
  • Mutagen - anything that can increase the rate of abnormal change in cells, which can lead to cancer
  • Mutation - a change in the genetic information within a cell
  • Myalgia - the medical term for muscle pain
  • Myasthenia gravis - a disease in which the muscles, mainly those in the face, eyes, throat, and limbs, become weak and tire quickly; caused by the body's immune system attacking the receptors in the muscles that pick up nerve impulses
  • Mycobacterium - a type of slow-growing bacterium; resistant to the body's defense mechanisms and are responsible for diseases such as tuberculosis and leprosy
  • Mycoplasma - the smallest free-living microorganisms
  • Mycosis - any disease caused by a fungus
  • Mydriatic - a drug that causes the pupil to dilate (widen)
  • Myelin sheath - the fat]] - and protein-containing material that surrounds and protects some nerves
  • Myelitis - inflammation of the spinal cord, which can cause headaches, fever, muscle stiffness, pain, weakness, and eventually paralysis
  • Myelocele - protrusion of the spinal cord and its coverings out from the spine; one of the more severe forms of spina bifida
  • Myeloma - a cancer affecting cells in the bone marrow; sometimes used as an abbreviation for multiple myeloma
  • Myelosclerosis - buildup of fibrous connective tissue in the bone marrow, affecting the production of blood components
  • Myocardial infarction - the death of an area of heart muscle as a result of being deprived of its blood supply; characterized by severe pain in the chest; commonly called a heart attack
  • Myocarditis - inflammation of the heart muscle, which can be caused by a virus, certain drugs, or radiation therapy
  • Myocardium - the medical term for heart muscle
  • Myomectomy - the surgical removal of a noncancerous tumor from muscle
  • Myopathy - a muscle disease, usually one that results in the deterioration of muscle
  • Myopia - the medical term for nearsightedness
  • Myositis - muscle inflammation, causing pain and weakness
  • Myringotomy - a surgical opening in the eardrum that allows for drainage
  • Myxoma - a noncancerous tumor made of mucous material and fibrous connective tissue
  • NSAID - see Nonsteroidal anti-inflammatory drug
  • Narcolepsy - a disorder that causes excessive sleepiness during the day and frequent and uncontrollable episodes of falling asleep
  • Narcosis - a drug (or other chemical)-induced drowsiness or stupor
  • Narcotic analgesics - a type of painkiller that blocks the transmission of pain signals in the brain; often cause tolerance (the need for higher amounts of the drug to produce the same effect) and drug dependence
  • Narcotic - an addictive substance that blunts the senses; can cause confusion, stupor, coma, and death with increased dosages
  • Nasal septum - the section of the nose that divides the left and right nostrils; made of cartilage and bone and covered by a mucous membrane
  • Nasogastric tube - a thin, plastic tube that is inserted through the nose, down the esophagus, and into the stomach; used to drain, wash, or take samples from the stomach, or to feed very sick patients who cannot eat
  • Nasopharynx - the passageway connecting the back of the nose to the top of the throat
  • Natural childbirth - a technique of giving birth that stresses relaxation techniques so that the use of pain-relieving drugs can be minimized; also called prepared childbirth
  • Natural methods of family planning - methods of planning a family that focus on a woman's time of ovulation, either so that pregnancy can be avoided or conception is likely
  • Nausea - feeling the need to vomit
  • Nebulizer - an instrument that provides a drug in its misted form through a face mask; used for severe asthma attacks and for children who have asthma but cannot use an inhaler
  • Necrosis - the medical term for the death of tissue cells
  • Needle aspiration - the use of a thin, hollow needle and syringe to remove body fluid for examination
  • Needle biopsy - the use of a hollow, wide-diameter needle to remove a sample of tissue for examination
  • Neonate - a term used to describe a newborn infant from birth to 1 month of age
  • Neoplasm - another term for a tumor
  • Nephrectomy - the surgical removal of one or both kidneys
  • Nephritis - inflammation of one or both kidneys because of an infection, an abnormal immune system response, or a disorder of metabolism
  • Nephroblastoma - a fast-growing cancer of the kidneys that occurs most commonly in children under 4 years of age
  • Nephrolithotomy - surgical removal of a kidney stone
  • Nephrons - the tiny filtering units of the kidney
  • Nephrosclerosis - the replacement of normal kidney structures with scar tissue
  • Nephrostomy - the surgical placement of a tube into the kidney to drain urine
  • Nephrotic syndrome - symptoms that result from damage to the filtering units of the kidney
  • Nerve block - the dulling of sensation in an area of the body by injecting a painkiller into or around a nerve leading to that section of the body
  • Nerve cell - the basic unit of the nervous system; transmits chemical messages throughout the body
  • Nerve compression - pressure on a nerve, which can cause nerve damage and muscle weakness
  • Nerve - a bundle of fibers that transmit electrical messages between the brain and areas of the body; these messages convey sensory or motor function information
  • Neural tube defects - problems in the development of the spinal cord and brain in an embryo, such as the failure of the spine to enclose the spinal cord (spina bifida) and the failure of the brain to develop (anencephaly)
  • Neural tube - the tube located along the back of an embryo that later develops into the spinal cord and brain
  • Neuralgia - pain along the course of a nerve caused by irritation or damage to the nerve
  • Neuritis - inflammation of a nerve, often characterized by pain, numbness, or tingling; also used to describe nerve damage and disease from causes other than inflammation
  • Neuroblastoma - a cancerous childhood tumor located in the adrenal glands or the sympathetic nervous system
  • Neurofibrillary tangles - abnormal spiral filaments on nerve cells in the brain; characteristic of Alzheimer disease
  • Neurofibromatosis - a condition in which connective tissue tumors occur on nerves in the skin
  • Neuroleptic - an antipsychotic drug
  • Neuroma - a noncancerous tumor occurring in nerve tissue
  • Neuron - another term for a nerve cell
  • Neuropathy - disease, inflammation, or damage to the nerves connecting the brain and spinal cord to the rest of the body
  • Neurosis - relatively mild emotional disorders (such as mild depression and phobias)
  • Neurotoxins - chemicals that attack and damage nerve cells
  • Neurotransmitters - chemicals that transfer messages from one nerve cell to another or from a nerve cell to a muscle cell
  • Neutrophil - a type of white blood cell
  • Nevus - a marking on the skin; can be present at birth (birthmark) or develop later (such as a mole)
  • Newborn respiratory distress syndrome - a disorder in which premature babies lack surfactant, a substance that stops the lungs from collapsing
  • Niacin - a vitamin important in many chemical processes in the body; also known as vitamin
  • Night terrors - a form of nightmlare causing abrupt awakening in terror; occurs mostly in children
  • Nitrates - a group of drugs that widen blood vessels; used to treat insufficient blood supply to the heart (angina pectoris) and reduced pumping efficiency of the heart (heart failure)
  • Nocturia - urination or a sleep-disturbing need to urinate during the night
  • Nocturnal emission - ejaculation of semen during sleep, which is normal in adolescent males; commonly called a wet dream
  • Node - a small, rounded tissue mass
  • Nodule - a small lump of tissue that is usually abnormal; can form under the skin or protrude
  • Non-Hodgkin's lymphoma - any cancer in lymphoid tissue (found mostly in the spleen and lymph glands) that is not Hodgkin's disease
  • Non-insulin-dependent diabetes - a type of diabetes mellitus that occurs mainly in those over 40 who are overweight; it is usually treated with diet changes and drugs that increase production of insulin by the pancreas (also known as type II diabetes mellitus)
  • Nondisjunction - an error that occurs during the division of sex chromosomes, causing either too much or too little genetic information to be placed in an egg or sperm when it is formed
  • Noninvasive - a term that is used to describe medical procedures that do not enter or penetrate the body; also refers to noncancerous tumors that do not spread to other sections of the body
  • Nonnarcotic analgesic - a drug that relieves pain by blocking the production of chemicals that stimulate pain-sensing nerves
  • Nonsteroidal anti-inflammatory drugs - a group of drugs that relieve pain and reduce inflammation
  • Norepinephrine - a hormone that regulates blood pressure by causing blood vessels to narrow and the heart to beat faster when blood pressure drops
  • Norwalk virus - a virus that causes acute gastroenteritis
  • Nosocomial infection - an infection acquired in a hospital
  • Nucleic acids - substances found in every living organism that provide the instructions for development; includes DNA and RNA
  • Nucleotide bases - molecules that form nucleic acids
  • Nucleus - the center or most important point of an object
  • Numbness - the lack of sensation in a part of the body because of interruption of nerve impulses
  • Nurse-midwife - a registered nurse who specializes in the care of a mother and child during pregnancy, labor, and delivery
  • Nutrient - any substance that the body can use to maintain its health
  • Nystagmus - persistent, rapid, involuntary movement of the eyes
  • OTC remedy - see Over-the-counter remedy
  • Oat cell carcinoma - another term for small-cell carcinoma
  • Obesity - a condition in which there is an excess of body fat; used to describe those who weigh at least 20 percent more than the maximum amount considered normal for their age, sex, and height
  • Obsessive-compulsive disorder - a mental disorder in which a person is obsessed with certain thoughts, leading them to repeatedly perform specific acts; for example, constantly washing the hands out of fear of germs and dirt
  • Obstructive sleep apnea - the blockage of the airways during sleep, which causes breathing to stop for very short periods of time, commonly caused by excessive relaxation of muscles at the back of the throat
  • Occlusion - the blocking of an opening or passageway in the body
  • Occult blood - blood in the feces that can be detected only by chemical tests
  • Occupational disease - a disease that occurs as a result of factors in the workplace
  • Occupational therapy - treatment to relearn physical skills lost as a result of an illness or accident
  • Ocular - describes something related to the eyes
  • Oculomotor nerves - nerves that stimulate movement of the eyeball
  • Olfactory nerves - nerves that play a role in the sense of smell
  • Oligodendroglioma - a rare type of cancerous brain tumor that occurs most commonly in the cerebrum
  • Oligohydramnios - an unusually small amount of amniotic fluid surrounding the fetus in the uterus, which can lead to complications with the pregnancy
  • Oligospermia - a low level of sperm in the semen; one of the main causes of infertility in men
  • Oncogenes - genes that, when altered by environmental factors or viruses, can cause abnormal cell growth
  • Oocyte - an egg cell that has not developed completely
  • Oophorectomy - the surgical removal of one or both ovaries; used to treat the growth of ovarian cysts or tumors
  • Open heart surgery - any operation in which the heart is stopped temporarily and a machine is used to take over its function of pumping blood throughout the body
  • Ophthalmia - severe inflammation of the eyes
  • Ophthalmologist - a doctor who specializes in care of the eyes; treats eye diseases and disorders
  • Ophthalmoplegia - partial or total loss of the ability to move the eyes
  • Ophthalmoscopy - examination of the inside of the eye using a lighted viewing instrument
  • Opportunistic infection - infection by organisms that would be harmless to a healthy person, but cause infection in those with a weakened immune system (for example, persons with AIDS or chemotherapy patients)
  • Optic nerves - the pair of nerves that carry visual information from the retina to the brain
  • Optic neuritis - inflammation of the optic nerve, often causing a partial loss of vision
  • Optic - pertaining to the eyes
  • Optician - a person who specializes in the making and adjustment of eyeglasses and contact lenses
  • Oral contraceptives - drugs taken in pill form to prevent pregnancy; contain synthetic progesterone and estrogen hormones
  • Orbit - the socket in the skull that contains the eyeball, along with its blood vessels, nerves, and muscles
  • Orchiectomy - the surgical removal of one or both of the testicles
  • Orchiopexy - an operation to correct an undescended testicle
  • Orchitis - inflammation of a testicle, which can be caused by infection with the mumps virus
  • Organ donation - an agreement to allow one or more organs to be removed and transplanted into someone else
  • Organism - any single, functioning form of life
  • Orgasm - involuntary contraction of genital muscles experienced at the peak of sexual excitement
  • Orphan drugs - drugs used to treat rare diseases; not normally produced because potential sales are small
  • Orthopnea - breathing difficulty experienced while lying flat; can be a symptom of heart failure or asthma
  • Orthotic - a device used to correct or control deformed bones, muscles, or joints
  • Osgood-Schlatter disease - painful enlargement and inflammation of the area of the shinbone just below the knee, usually occurring in adolescent boys
  • Osmosis - the process of passage of the solvent portion of a lesser-concentrated solution through a semipermeable membrane into a higher-concentrated solution until the two solutions are equal in concentration; plays an important role in water distribution in the body
  • Ossification - the formation and maintenance of bone
  • Osteitis deformans - another name for Paget's disease
  • Osteitis - inflammation of bone
  • Osteoarthritis - see Degenerative arthritis
  • Osteoblast - a cell that forms bone
  • Osteochondritis dissecans - bone degeneration inside of a joint, causing small pieces of bone and cartilage to become detached
  • Osteochondritis juvenilis - inflammation of a growing section of bone in a child or adolescent
  • Osteochondroma - a noncancerous tumor made up of bone and cartilage
  • Osteoclast - a cell that breaks down unwanted bone tissue; also refers to a device for fracturing a bone to correct a deformity
  • Osteodystrophy - defective bone formation
  • Osteogenesis imperfecta - a genetic disorder in which bones are abnormally fragile, leading to multiple breaks and deformity
  • Osteolysis - the softening and destruction of bone
  • Osteoma - a noncancerous bone tumor
  • Osteomalacia - the loss of minerals and softening of bones because of a lack of vitamin D; called rickets in children
  • Osteomyelitis - the inflammation of bones and bone marrow because of an infection, usually caused by bacteria
  • Osteopetrosis - a rare hereditary disorder in which bones become harder and more dense, causing them to break more easily
  • Osteophyte - an outgrowth of bone near a joint
  • Osteoporosis - a condition in which bones become less dense, more brittle, and fracture easily
  • Osteosarcoma - a cancerous bone tumor
  • Osteosclerosis - an abnormal increase in density and hardness of bone
  • Otalgia - the medical term for an earache
  • Otitis externa - inflammation of the outer ear due to an infection; commonly called swimmer's ear
  • Otitis media - inflammation of the middle ear (between the eardrum and inner ear) because of the spread of an infection from the nose, sinuses, and throat
  • Otorrhea - a discharge from an inflamed ear
  • Otosclerosis - progressive deafness caused by bone formation around structures in the middle ear
  • Ototoxicity - harmful effect that some drugs have on the organs or nerves in the ears, which can lead to hearing and balance problems
  • Outpatient treatment - medical attention that does not include an overnight stay at a hospital
  • Ovaries - two almond-shaped glands located at the opening of the fallopian tubes on both sides of the uterus; produce eggs and the sex hormones estrogen and progesterone
  • Over-the-counter remedy - a medication that can be purchased without a physician's prescription
  • Overdose - an excessively large dose of a drug, which can lead to coma and death
  • Ovulation - the development and release of the egg from the ovary, which usually occurs halfway through a woman's menstrual cycle
  • Ovum - another term for an egg cell
  • Oxidation - a chemical reaction involving active sources of oxygen (called oxygen free radicals) that damages cells
  • Oximetry - determination of the amount of oxygen in the blood by measuring the amount of light transmitted through an area of skin
  • Oxygen free radicals - active forms of oxygen found in pollution, cigarette smoke, and radiation that can damage cells and are believed to play a role in the aging process and cancer
  • Oxygen - a gas that is colorless, odorless, and tasteless; essential to almost all forms of life
  • Oxytocin - a hormone produced in the pituitary gland that causes contraction of the uterus during childbirth and stimulation of milk flow during breast-feeding
  • Ozone - a poisonous form of oxygen that is present in the earth's upper atmosphere, where it helps to screen the earth from damaging ultraviolet rays
  • PET scanning - see Positron emission tomography scanning
  • PID - see Pelvic inflammatory disease
  • PKU - see Phenylketonuria
  • PMS - see Premenstrual syndrome
  • PUVA - a form of phototherapy that combines the use of psoralens and ultraviolet light to treat skin disorders
  • Pacemaker - a small electronic device that is surgically implanted to stimulate the heart muscle to provide a normal heartbeat
  • Paget's disease - a disorder occurring in the middle-aged and elderly in which bone does not form properly, causing bone weakening, thickening, and deformity
  • Palate - the roof of the mouth
  • Palliative treatment - treatment that relieves the symptoms of a disorder without curing it
  • Pallor - abnormally pale skin; usually refers to the skin of the face
  • Palpation - the use of the hands to feel parts of the body to check for any abnormalities
  • Palpitation - an abnormally rapid and strong heartbeat
  • Palsy - loss of sensation or ability to move
  • Pancreas - a long gland located behind the stomach that produces enzymes that help to break down food and hormones (insulin and glucagon) that help to regulate glucose levels in the blood
  • Pancreatitis - inflammation of the pancreas, which is often caused by alcohol abuse
  • Pandemic - a widespread epidemic
  • Panic disorder - an emotional disorder characterized by attacks of anxiety that have no normal causes; usually made worse by stress
  • Pap smear - a test in which cells are scraped off the cervix and examined for abnormalities; used to detect changes that might precede cervical cancer and to diagnose viral infections such as herpes simplex
  • Papilloma - a tumor occurring on the skin or mucous membranes; usually not cancerous
  • Paracentesis - the insertion of a needle into a body cavity to relieve pressure, inject a drug, or remove a sample for analysis
  • Paralysis - the inability to use a muscle because of injury to or disease of the nerves leading to the muscle
  • Paramedic - a person trained to give first aid and other emergency medical care
  • Paranoia - a disorder in which a person becomes overly suspicious and emotionally sensitive
  • Paraphimosis - strangulation of the head of the penis by a tight or inflamed foreskin that has been pulled back
  • Paraplegia - complete or partial loss of sensation and movement of the legs
  • Parasite - an organisms that lives on or in other organisms, from which it obtains nutrients
  • Parasympathetic nervous system - the part of the autonomic nervous system that is stimulated during times of relaxation
  • Parathyroid glands - small glands located in the neck that produce a hormone that regulates the levels of calcium in the blood
  • Parathyroid hormone - a hormone released by the parathyroid glands that plays a role in controlling calcium levels in the blood
  • Parathyroidectomy - the surgical removal of one or more of the parathyroid glands
  • Parenteral - the introduction of a substance into the body by any route other than the digestive tract, such as through a vein or muscle
  • Paresis - partial paralysis
  • Paresthesia - numbness or tingling in the skin; commonly referred to as "pins and needles"
  • Parkinson's disease - a brain disorder in which there is a lack of the chemical messenger dopamine, which helps control muscle movement; leads to muscle stiffness, weakness, and trembling
  • Paronychia - a bacterial or yeast infection of the skin around the nail
  • Parotid glands - salivary glands located in the mouth near the ears
  • Paroxysm - a sudden attack or worsening of a disease's symptoms
  • Partial mastectomy - a treatment for breast cancer in which a tumor is removed, along with the skin covering it and some of the surrounding tissues and muscles
  • Partial seizure - an abnormal electrical discharge in a certain area of the brain, affecting only certain functions
  • Passive exercise - exercise of an injured part of the body involving no effort from that injured part
  • Passive smoking - a nonsmoker inhaling the cigar, cigarette, or pipe smoke of others (called second-hand smoke) in the same area, which increases the nonsmoker's risk of cancer and respiratory disorders
  • Patella - the medical term for the kneecap
  • Patent ductus arteriosus - a genetic disorder of the heart in which a channel connecting the pulmonary artery and the aorta fails to close and the heart must work harder to supply the body with blood
  • Patent - not obstructed; open
  • Paternity testing - use of blood tests to match up DNA or specific blood proteins to determine whether a man is the father of a child
  • Pathogen - any substance capable of causing a disease; usually refers to a disease-causing microorganism
  • Pathogenesis - the production and development of a disease or disorder
  • Pathology - the study of disease
  • Patient-controlled analgesia - a system for administering pain-killing drugs in which the amount of drug delivered is controlled by the patient
  • Peak flow measurement - the maximum speed that air is exhaled from the lungs; used to diagnose asthma or to determine the effectiveness of asthma medications
  • Pectoral muscles - the muscles of the upper part of the chest that move the arm across the body, raise some of the ribs, and move the shoulders
  • Pellagra - a deficiency of the vitamin niacin; causes dermatitis, diarrhea, and mental disorders
  • Pelvic examination - an examination of a woman's reproductive organs
  • Pelvic inflammatory disease - inflammation of a woman's internal reproductive organs, usually as a result of a bacterial infection; one of the most common causes of pelvic pain and infertility in women
  • Pelvis - the group of bones in the lower part of the trunk that support the upper body and protect the abdominal organs
  • Penile function tests - tests used to determine the cause of impotence, including blood tests and nerve function tests
  • Penile implant - an inflatable device surgically inserted into the penis that allows a man with impotence to have sexual intercourse
  • Penis - the external male reproductive organ, which passes urine and semen out of the body
  • Pepsin - the enzyme found in gastric juice that helps digest protein
  • Peptic ulcer - an erosion in the lining of the esophagus, stomach, or small intestine, usually caused in part by the corrosive action of gastric acid
  • Percutaneous - a procedure that is performed through the skin, such as an injection
  • Perforation - a hole in an organ or body structure caused by disease or injury
  • Periarteritis nodosa - inflammation and weakening of small and medium arteries
  • Pericardial effusion - fluid buildup inside of the pericardium, affecting the performance of the heart
  • Pericarditis - inflammation of the membranous sac that covers the heart, causing chest pain and fever
  • Pericardium - the membranous sac that covers the heart and the base of the blood vessels that are attached to the heart
  • Perinatal - occurring just before or just after birth
  • Periosteum - the tissue covering bones, except the surfaces in joints
  • Periostitis - inflammation of the periosteum
  • Peripheral nervous system - the nerves that branch out from the brain and spinal cord to the rest of the body
  • Peripheral vascular disease - the narrowing of blood vessels in the legs or arms, causing pain and possibly tissue death (gangrene) as a result of a reduced flow of blood to areas supplied by the narrowed vessels
  • Peristalsis - wavelike movement of smooth muscle-containing tubes, such as the digestive tract
  • Peritoneum - the membrane that lines the abdominal cavity and covers the abdominal organs
  • Peritonitis - inflammation of the peritoneum
  • Pernicious anemia - an anemia caused by a failure to absorb vitamin B12; which is essential in the production of normal red blood cells
  • Perthes' disease - inflammation of the growing head of a femur; a type of osteochondritis juvenilis
  • Pertussis - a bacterial infection of the respiratory tract characterized by short, convulsive coughs that end in a whoop sound when breath is inhaled (commonly called whooping cough); mainly affects children
  • Petit mal - a seizure characterized by loss of awareness for brief periods
  • Peutz-Jeghers syndrome - a genetic disorder in which there are polyps in the small intestine and brown melanin spots on the lips, mouth, fingers, and toes pH]] - a measure of the acidic or basic character of a substance
  • Phagocyte - an immune system cell that can surround and digest foreign bodies, unwanted cellular material, and microorganisms
  • Phantom limb - the sensation of a limb after it has been amputated
  • Pharmacology - the study of medications, including drug development
  • Pharyngitis - inflammation of the throat (the pharynx), causing sore throat, fever, earache, and swollen glands
  • Pharynx - the throat; the tube connecting the back of the mouth and nose to the esophagus and windpipe
  • Phenothiazines - a group of drugs used as antipsychotics, antihistamines, and antiemetics
  • Phenylketonuria - a hereditary disorder in which the enzyme that converts the amino acid phenylalanine into another amino acid is defective, meaning phenylalanine must be kept out of the diet
  • Pheochromocytoma - a noncancerous tumor of cells that produce epinephrine and norepinephrine, causing higher levels of these hormones in the blood and an increase in blood pressure
  • Phimosis - tightness of the foreskin, which prevents it from being moved back over the head of the penis
  • Phlebitis - inflammation of a vein
  • Phlebothrombosis - formation of a blood clot in a vein
  • Phlegm - mucus and other material produced by the lining of the respiratory tract; also called sputum
  • Phobia - a persisting fear of and desire to avoid something
  • Phosphates - salts containing phosphorus; essential to some body functions such as the bones and teeth
  • Phospholipids - fatty substances that make up the membranes surrounding cells
  • Phosphorus - a mineral that is an important part of structures such as bones, teeth, and membranes in the body; also involved in numerous other chemical reactions
  • Photocoagulation - tissue destruction using a focused beam of light
  • Photophobia - an abnormal sensitivity of the eyes to light
  • Photosensitivity - an abnormal reaction to sunlight, which usually occurs as a rash
  • Phototherapy - treatment with some form of light
  • Physical therapy - the treatment of injuries or disorders using physical methods, such as exercise, massage, or the application of heat
  • Physiology - the study of the body’s functions
  • Phytochemicals - chemicals in plants that might help protect against disorders such as cancer
  • Pica - a desire to eat materials that are not food
  • Pickwickian syndrome - extreme obesity along with shallow breathing, sleep apnea, excessive sleepiness, and heart failure
  • Pigmentation - the coloration of the skin, hair, and eyes by the pigment melanin
  • Pinkeye - inflammation of the membrane that covers the white of the eyes and lines the eyelids, causing redness, discomfort, and a discharge; can be caused by infection or allergies
  • Pinworm - a small parasite worm that can live in the intestines; commonly affects children
  • Pituitary adenoma - a noncancerous tumor of the pituitary gland
  • Pituitary gland - a small, round gland located at the base of the brain that releases hormones that control other glands and body processes
  • Pityriasis alba - a common childhood or adolescent disorder in which there are pale, scaly patches on the skin of the face
  • Pityriasis rosea - a mild skin condition in which flat, scaly spots occur on the trunk and upper arms
  • Pivot joint - a joint designed for rotational movement
  • Placebo effect - the positive or negative response to a drug that is caused by a person's expectations of a drug rather than the drug itself
  • Placebo - a chemically inactive substance given in place of a drug to test how much of a drug's effectiveness can be attributed to a patient's expectations that the drug will have a positive effect
  • Placenta previa - a disorder in which the placenta develops at the lower section of the uterus (close to or covering the cervix); varies in severity, from no effect on a pregnancy to vaginal bleeding and danger to the mother and the fetus
  • Placenta - an organ formed in the uterus during pregnancy that links the blood of the mother to the blood of the fetus; provides the fetus with nutrients and removes waste
  • Placental abruption - the separation of the placenta from the wall of the uterus before childbirth, which causes severe bleeding that threatens the life of the mother and the fetus
  • Placental insufficiency - a disorder occurring during pregnancy in which the placenta does not function properly, causing the fetus to be deprived of nutrients
  • Plague - a serious infectious disease transmitted to humans through bites of rodent fleas
  • Plantar reflex - the normal curling of the toes downward when the sole of the foot is stroked
  • Plantar wart - a rough-surfaced, hard spot on the sole of the foot that is caused by a virus
  • Plaque - an area of buildup of fat deposits in an artery, causing narrowing of the artery and possibly heart disease; dental plaque refers to a coating on the teeth, consisting of saliva, bacteria, and food debris, which causes tooth decay
  • Plasma cell - a white blood cell that makes antibodies
  • Plasma - the liquid part of the blood, containing substances such as nutrients, salts, and proteins
  • Plasmapheresis - a procedure for removing unwanted substances from the blood in which blood is drawn, its plasma is separated and replaced, and the cleansed blood is returned to the body
  • Platelet - the smallest particle found in the blood, which plays a major role in forming blood clots
  • Pleura - the double-layered membrane that lines the lungs and chest cavity and allows for lung movement during breathing
  • Pleural effusion - a buildup of fluid between the membranes that line the lungs and chest cavity (the pleura); causes compression of the lungs, which leads to breathing difficulty
  • Pleural membranes - the pleura
  • Pleural rub - a rubbing sound produced by inflamed pleural membranes that can be heard when breathing
  • Pleural space - the space between the two layers of the pleura
  • Pleurisy - inflammation of the lining of the lungs and chest cavity, usually caused by a lung infection; characterized by sharp chest pain
  • Pleurodynia - pain in the chest caused by a virus
  • Plummer-Vinson syndrome - difficulty swallowing due to an abnormal web of tissue across the upper part of the esophagus
  • Pneumoconiosis - a respiratory disease caused by dust inhalation
  • Pneumocystis pneumonia - an opportunistic infection of the lungs caused by a singlecelled parasite
  • Pneumonectomy - surgical removal of a lung
  • Pneumonia - inflammation of the lungs due to a bacterial or viral infection, which causes fever, shortness of breath, and the coughing up of phlegm
  • Pneumothorax - a condition in which air enters the space between the chest wall and the lungs, causing chest pain and shortness of breath; may occur spontaneously or be the result of a disease or an accident
  • Poliomyelitis - an infectious disease caused by a virus; usually causes only mild symptoms but in rare cases can attack the brain and spinal cord and cause paralysis or death
  • Polyarthritis - arthritis occurring in more than one joint
  • Polycystic kidney disease - a condition in which there are multiple, slow-growing cysts on both kidneys
  • Polycystic ovary syndrome - a hereditary disease characterized by multiple cysts on the ovaries, obesity, excessive hairiness, infertility, and irregular menstruation
  • Polycythemia - an increased amount of red blood cells in the blood
  • Polydactyly - the presence of an excessive number of fingers or toes
  • Polydipsia - excessive thirst
  • Polymyalgia rheumatica - a rare disease of the elderly, characterized by muscle stiffness and pain in the hips, thighs, shoulders, and neck
  • Polymyositis - an autoimmune disease of connective tissue in which muscles weaken and become inflamed
  • Polyp - a growth that occurs on mucous membranes such as those in the nose and intestine; bleeds easily and can become cancerous
  • Polysaccharide - a complex carbohydrate composed of three or more simple carbohydrate molecules joined together
  • Polyunsaturated fat - a fat or oil that contains well below the maximum number of hydrogen atoms possible; thought to reduce the risk of coronary heart disease
  • Polyuria - the excessive production of urine; can be a symptom of various diseases, most notably diabetes mellitus
  • Porphyria - a group of genetic disorders in which substances called porphyrins build up in the blood, often causing rashes brought on by exposure to sunlight and reactions to certain drugs
  • Portal hypertension - increased blood pressure in the portal vein
  • Portal vein - the vein connecting the stomach, intestines, and spleen to the liver
  • Positron emission tomography scanning - an imaging method in which substances emitting positrons (positively charged particles) are introduced into the body, and detectors connected to a computer are used to form images of the tissues
  • Post-traumatic stress disorder - feelings of anxiety experienced after a particularly frightening or stressful event, which include recurring dreams, difficulty sleeping, and a feeling of isolation
  • Postcoital contraception - the prevention of pregnancy after sexual intercourse has occurred
  • Posterior - describes something that is located in or relates to the back of the body
  • Postmenopausal bleeding - bleeding from the vagina that occurs after menopause
  • Postmortem examination - examination of a body after death to determine the cause of death; commonly called an autopsy
  • Postmyocardial infarction syndrome - a condition that occurs following a heart attack or heart surgery; characterized by fever, chest pain, pericarditis, and pleurisy
  • Postnatal - describes something that occurs after birth, usually to the baby
  • Postpartum - a term that describes something that occurs after childbirth, usually to the mother
  • Postural drainage - drainage of mucus from specific areas of the lungs by placing the body in a specific position
  • Postural hypotension - unusually low blood pressure that occurs after suddenly standing or sitting up
  • Potassium - a mineral that plays an important role in the body, helping to maintain water balance, normal heart rhythm, conduction of nerve impulses, and muscle contraction
  • Precancerous - describes a condition from which cancer is likely to develop
  • Precordial movement - movement of the heart that is seen and felt through the chest wall
  • Preeclampsia - a serious disorder that occurs in the second half of pregnancy, in which a woman experiences high blood pressure, fluid retention, nausea, and headaches; if not treated it can lead to eclampsia
  • Premature labor - labor that begins before the full term of pregnancy (about 37 weeks)
  • Premature rupture of membranes - the rupture of the sac that holds the fluid surrounding the fetus before the full term of pregnancy (about 37 weeks)
  • Premedication - drugs, usually painkillers, taken 1 to 2 hours before surgery
  • Premenopausal - a term that describes the period of a few years in a woman's life just before menopause
  • Premenstrual syndrome - physical and emotional changes that occur in a woman 1 or 2 weeks before menstruation, at or after ovulation; characterized by irritability, tension, depression, and fatigue
  • Prenatal care - medical care of a pregnant woman and the fetus
  • Prenatal diagnosis - techniques used to diagnose abnormalities in a fetus
  • Prenatal testing - tests performed on a pregnant woman or her fetus to prevent or diagnose abnormalities
  • Prepared childbirth - a technique in which a pregnant woman tries to minimize use of pain-relief medications during childbirth by learning relaxation techniques
  • Prepuce - the foreskin
  • Presbycusis - the loss of hearing that occurs naturally with age
  • Presbyopia - the loss of the ability to focus the eyes on near objects that occurs naturally with age, as a result of loss of elasticity of the lens of the eyes
  • Pressure point - specific points on the body where external pressure can be applied to prevent excessive arterial bleeding
  • Pressure sore - an ulcer (erosion) on the skin that is a result of being bedridden; commonly called a bedsore
  • Priapism - a painful, persistent erection without sexual arousal, requiring emergency treatment
  • Prickly heat - a rash involving small, red, itchy spots and a prickly sensation that usually appears where sweat builds up
  • Primary - a disease that began in the affected location
  • Prion - an agent that is believed to cause several degenerative brain diseases
  • Procidentia - severe prolapse of an organ
  • Proctalgia - pain in the rectum
  • Proctitis - inflammation of the rectum, which causes soreness and sometimes mucus and/or pus in the stool
  • Proctoscopy - examination of the rectum using a viewing instrument
  • Productive cough - a cough that brings up phlegm, which is the body's natural way of clearing blocked airways
  • Progeria - an extremely rare condition in which the body ages prematurely
  • Progesterone - a female sex hormone that plays many important roles in reproduction, including the thickening of the lining of the uterus during the menstrual cycle; and during pregnancy, the functioning of the placenta, and the initiation of labor
  • Prognosis - a doctor's probable forecast of the effects and outcome of a disease
  • Progressive muscular atrophy - gradual degeneration and weakening of muscles due to a degenerative spinal cord
  • Prolactin - a hormone released by the pituitary gland that is responsible for the development of breasts and milk production in females
  • Prolapse - the displacement of an organ from its normal position to a new one
  • Prolapsed disk - see Disk prolapse
  • Prophylactic - anything used to prevent disease
  • Proprioception - the body's system for determining its position relative to the outside world
  • Prostate gland - an organ located under the bladder that produces a large part of the semen
  • Prostatectomy - the partial or complete surgical removal of the prostate gland
  • Prostatism - symptoms caused by an enlarged prostate gland, including difficulty with urination
  • Prostatitis - inflammation of the prostate gland, usually due to a bacterial infection spread from the urethra
  • Prosthesis - an artificial replacement for a missing part of the body
  • Proteins - large molecules made up of amino acids that play many major roles in the body, including forming the basis of body structures such as skin and hair, and important chemicals such as enzymes and hormones
  • Prothrombin time - the time it takes for a sample of blood to clot after substances that speed clotting time have been added; used to measure the effect of anticoagulants
  • Proto-oncogene - a gene that is normally inactive but can become a cancer-causing oncogene if made active
  • Proton pump inhibitor - a drug used to treat peptic ulcers that reduces the amount of gastric acid produced
  • Protozoan - a simple, single-celled organism
  • Proximal - located nearer to a central point of reference on the body, such as the trunk
  • Pruritus - the medical term for itching
  • Pseudogout - a form of arthritis with symptoms similar to gout that results from the depositing of calcium salts in a joint
  • Pseudomembranous enterocolitis - severe inflammation of the colon as a result of antibiotic use by an immunocompromised individual
  • Psittacosis - a chlamydial infection resembling influenza that is spread to humans by the droppings of infected birds
  • Psoralens - drugs that contain chemicals derived from plants; used to treat the skin disorders psoriasis and vitiligo
  • Psoriasis - a skin disorder characterized by patches of thick, red skin often covered by silvery scales
  • Psoriatic arthritis - a form of arthritis that develops as a complication of the skin disorder psoriasis
  • Psychogenic - resulting from psychological or emotional disorders
  • Psychological - relating to the mind and the processes of the mind
  • Psychosis - a mental disorder in which a serious inability to think, perceive, and judge clearly causes loss of touch with reality
  • Psychosomatic - describes a physical condition that is influenced by psychological or emotional factors
  • Psychotherapy - the treatment of mental and emotional disorders using psychological methods, such as counseling, instead of physical means
  • Psychotic - relating to psychosis
  • Psychotropic drug - a drug that has a psychological effect
  • Ptosis - the drooping of the upper eyelid
  • Puberty - the period of time (usually between the ages of 10 and 15) during which sexual development occurs, allowing reproduction to become possible
  • Pubic louse - a small insect that lives in pubic hair, feeds on blood, and is usually spread by sexual contact; pubic lice are popularly called "crabs"
  • Pudendal block - a local anesthesia procedure used during childbirth, causing the lower part of the vagina to be insensitive to pain
  • Pudendum - the external genitals, usually referring to the female
  • Puerperal sepsis - infection of the female genital tract following childbirth, abortion, or miscarriage
  • Puerperium - the time period after childbirth (about 6 weeks) during which a woman's body returns to its normal physical state
  • Pulmonary artery - the artery that supplies the lungs with blood from the heart
  • Pulmonary edema - the buildup of fluid in lung tissue, which is usually caused by heart failure
  • Pulmonary embolism - blockage of the pulmonary artery by a floating mass in the blood
  • Pulmonary fibrosis - a condition in which the tissue of the lungs has become thick and scarred, usually because of inflammation caused by lung conditions such as pneumonia or tuberculosis
  • Pulmonary heart valve - the heart valve that stops blood pumped to the lungs from leaking back into the heart
  • Pulmonary hypertension - increased blood pressure in the arteries supplying blood to the lungs; caused by increased resistance to blood flow in the lungs, usually a result of a lung disease
  • Pulmonary insufficiency - a rare defect in the pulmonary heart valve in which it fails to close properly after each muscle contraction, allowing blood to leak back into the heart; weakens the heart's pumping ability
  • Pulmonary stenosis - obstruction of the flow of blood from the heart to the lungs
  • Pulp - the soft tissue inside of a tooth that contains blood vessels and nerves
  • Pulse - the expansion and contraction of a blood vessel due to the blood pumped through it; determined as the number of expansions per minute
  • Pupil - the opening at the center of the iris in the eye that constricts (contracts) and dilates (widens) in response to light
  • Purpuric rash - areas of purple or reddish-brown spots on the skin, which are caused by bleeding from underlying tissues
  • Pus - a thick, yellowish or greenish fluid that contains dead white blood cells, tissues, and bacteria; occurs at the site of a bacterial infection
  • Pustule - a small blister containing pus
  • Pyelolithotomy - surgical removal of a kidney stone
  • Pyelonephritis - inflammation of the kidney, usually due to a bacterial infection
  • Pyloric sphincter - a circular muscle located at the junction of the stomach and small intestine that controls the passage of food into the small intestine
  • Pyloric stenosis - narrowing of the outlet located at the junction of the stomach and small intestine
  • Pyloroplasty - surgical widening of the outlet between the stomach and small intestine
  • Pyrexia - a body temperature of above 98.6°F in the mouth or 99.8°F in the rectum
  • Pyrogen - any substance that causes a fever
  • Pyuria - the presence of white blood cells in the urine; usually an indication of kidney or urinary tract infection
  • Quadriceps muscle - the muscle (consisting of 4 distinct parts) located at the front of the thigh that straightens the leg
  • REM sleep - rapid eye movement sleep; the stage of sleep in which dreaming occurs
  • RNA - ribonucleic acid, which helps to decode and process the information contained in DNA
  • Rabies - an infectious viral disease primarily affecting animals; can be transmitted to humans through an infected animal's bite; if untreated, can result in paralysis and death
  • Radial keratotomy - a surgical procedure for correcting nearsightedness in which tiny cuts are made in the cornea to change its shape and focusing properties
  • Radiation therapy - treatment of a disease, such as cancer, using forms of radioactivity that damage or destroy abnormal cells
  • Radiation - a variety of types of energy, such as X-rays and ultraviolet
  • Radical surgery - treatment of disease by surgically removing all tissue that is or may be affected
  • Radiculopathy - any disease of the nerve roots; can be caused by disk prolapse, arthritis, and other problems
  • Radioallergosorbent test - a blood test performed to help determine the cause of an allergy by detecting the presence of antibodies to various allergens
  • Radiography - the formation of images of the inside of the body using radiation projected through the body and onto film; a radiograph is also called an X-ray
  • Radionuclide scanning - an imaging technique in which a radioactive substance is introduced into the body and its emitted radiation is detected; specific organs can be studied according to the amount of the radioactive substance that they absorb
  • Radius - one of the two long bones of the forearm, located on the thumb side of the arm
  • Radon - a colorless, odorless, tasteless radioactive gas that is produced by materials in soil, rocks, and building materials; suspected of causing cancer
  • Rales - abnormal crackling or bubbling sounds heard in the lungs during breathing
  • Rash - an area of inflammation or a group of spots on the skin
  • Raynaud's disease - a condition in which the fingers and toes become pale when exposed to cold or emotional stress, owing to sudden narrowing of the arteries that supply them with blood
  • Receptor - a nerve cell that responds to a stimulus and produces a nerve impulse; also refers to the area on the surface of a cell that a chemical must bind to in order to have its effect
  • Recessive gene - a gene that does not produce its effect when it occurs with a dominant gene, but produces its effect only when there are two copies of it
  • Reconstructive surgery - surgery to rebuild part of the body that has been damaged or defective from birth
  • Rectal prolapse - bulging of the lining of the rectum through the anus, usually due to straining during a bowel movement
  • Rectum - a short tube located at the end of the large intestine, which connects the intestine to the anus
  • Red blood cell - a doughnut-shaped blood cell that carries oxygen from the lungs to body tissues
  • Reduction of fracture - the realignment of the broken ends of a bone
  • Referred pain - pain felt in a part of the body remote from the site where pain originates
  • Reflex - an automatic, involuntary response of the nervous system to a stimulus
  • Reflux esophagitis - the backflow of gastric acid from the stomach to the lower esophagus, owing to a defect in the valve that separates them
  • Regurgitation - the backflow of fluid; can refer to food and drink flowing back up from the stomach into the mouth or blood flowing back into the heart through a defective heart valve
  • Rehabilitation - treatment for an injury or illness aimed at restoring physical abilities
  • Rehydration - treatment for dehydration (an abnormally low level of water in the body) in which levels are restored by taking fluids containing water, salt, and glucose by mouth or, if severe, through a vein
  • Reiter's syndrome - a disorder characterized by inflammation of the joints, urethra, and sometimes the conjunctiva
  • Relapse - the return of a disease or symptom after it had disappeared
  • Remission - the temporary disappearance of a disease or its symptoms, either partially or completely; also refers to the time period in which this occurs
  • Renal cell carcinoma - the most common type of kidney cancer
  • Renal colic - severe pain on one side of the lower back, usually as a result of a kidney stone
  • Renal tubular acidosis - inability of the kidneys to remove sufficient amounts of acid from the body, making the blood more acidic than normal
  • Renin - an enzyme that plays a role in increasing a low blood pressure
  • Repetitive strain injury - an injury that occurs when the same movement is repeated continuously
  • Reproductive system - the organs and structures that allow men and women to have sexual intercourse and produce children
  • Resection - partial or complete surgical removal of a diseased organ or structure
  • Respiration - the process by which oxygen is taken in and used by tissues in the body and carbon dioxide is released
  • Respirator - another term for a ventilator
  • Respiratory arrest - a condition in which a person suddenly stops breathing
  • Respiratory distress syndrome - a condition experienced after an illness or injury damages the lungs, causing severe breathing difficulty and resulting in a life-threatening lack of oxygen in the blood
  • Respiratory failure - the failure of the body to exchange gases properly, which leads to a buildup of carbon dioxide and a lack of oxygen in the blood
  • Respiratory system - the organs that carry out the process of respiration
  • Resting pulse - the pulse rate when a person is not experiencing any physical activity or mental stress
  • Reticulocyte - an immature red blood cell
  • Retina - a membrane lining the inside of the back of the eye that contains light-sensitive nerve cells that convert focused light into nerve impulses, making vision possible
  • Retinal artery occlusion - obstruction of an artery that supplies blood to the retina, resulting in some degree of temporary or permanent blindness
  • Retinitis pigmentosa - gradual loss of the field of vision, owing to a degeneration of the light-sensitive nerve cells of the retina
  • Retinoblastoma - a hereditary, cancerous tumor of the retina affecting infants and children
  • Retinoid - a substance resembling vitamin A that is used to treat skin conditions such as acne and has been reported to reduce skin wrinkling
  • Retinopathy - any disease or disorder of the retina; usually refers to damage to the retina caused by high blood pressure or diabetes mellitus
  • Retinoscopy - a method of determining focusing errors of the eye in which light is shined through the pupil and the reflected beam is measured
  • Retroviruses - a group of viruses that are made up of RNA instead of DNA, including HIV and the virus that causes T-cell leukemia
  • Reye's syndrome - a rare disorder mainly affecting those under the age of 15 that is characterized by brain and liver damage following a viral infection such as chickenpox or the flu; may be linked to taking aspirin to treat a viral infection
  • Rh blood group - a blood group classifying whether the substances called Rhesus (Rh) factors are present on the surface of red blood cells; the "positive" or "negative" designation in blood classification (for example, "O negative")
  • Rh immunoglobulin - a substance used to prevent a woman who is Rh incompatible with her fetus from becoming Rh sensitized
  • Rh incompatibility - a condition in which a pregnant woman's Rh factor does not match that of the fetus; can lead to the production of antibodies by the mother that destroy the fetus' red blood cells
  • Rh sensitized - a condition in which a woman who has a negative Rh factor develops permanent antibodies against Rh-positive blood as a result of exposure to the blood of her fetus; can cause fetal hemolysis in subsequent pregnancies
  • Rheumatic fever - a disorder that follows a throat infection by the streptococcus bacteria and causes inflammation in body tissues
  • Rheumatoid arthritis - a condition in which joints in the body become inflamed, stiff, painful, and sometimes deformed because of the body's own immune system attacking the tissues
  • Rheumatoid factors - antibodies that are present in about 80% of people with rheumatoid arthritis; their detection through blood testing can help to diagnose the disorder
  • Rhinitis - inflammation of the mucous membrane lining the nose, which can cause sneezing, runny nose, congestion, and pain; when caused by substances in the air, it is called allergic rhinitis or hay fever
  • Rhinophyma - a bulb-shaped deformity and redness of the nose as a result of severe rosacea
  • Rhinoplasty - surgery that changes the structure of the nose, either to improve appearance or to correct a deformity or injury
  • Rhythm method - a method of preventing pregnancy in which a couple does not have sexual intercourse during the days of the menstrual cycle during which fertilization can occur
  • Riboflavin - a vitamin belonging to the vitamin B complex that is important in many processes in the body and helps to maintain healthy skin
  • Rickets - a childhood disease in which bones lack calcium and are deformed as a result of vitamin D deficiency (vitamin D helps the body absorb calcium)
  • Rigor mortis - the stiffness that occurs in the body after death
  • Ringworm - a skin infection caused by a fungus that spreads out in an even circle, characterized by ring-like, scaly patches of red skin
  • Rinne's test - a test that uses a tuning fork to diagnose hearing loss resulting from poor conduction of sound from the outer to the inner ear
  • Rocky mountain spotted fever - a rare disease transmitted to humans through the bites of ticks; characterized by small pink spots on the wrists and ankles that spread to other parts of the body, become larger, and bleed
  • Rosacea - a skin disorder that is characterized by patches of red skin on the nose and cheeks and acne-like bumps; most commonly occurs in middle-aged women
  • Roseola infantum - a common disease in young children characterized by a sudden fever and rash
  • Rotator cuff - a structure made up of four muscle tendons that reinforces the shoulder joint
  • Roundworm - a group of worms that includes many of the major human parasites
  • Rubella - a mild viral infection (also known as German measles) that produces a rash and fever; dangerous when it infects a woman during the early stages of pregnancy, when it can spread causing birth defects in the fetus
  • Rubeola - another term for measles
  • Rupture - a tear or break in an organ or tissue
  • SADS - see Seasonal affective disorder syndrome
  • SIDS - see Sudden infant death syndrome
  • SPECT - see Single photon emission computed tomography
  • STD - see Sexually transmitted disease
  • Saccharides - a group of carbohydrates, including sugars and starches
  • Sacroiliac joints - the pair of joints located in the pelvis between the sacrum and the hipbones
  • Sacroiliitis - inflammation of the sacroiliac joints, which causes pain in the lower body
  • Sacrum - the triangular bone located at the bottom of the spine that is connected to the tailbone, the hipbones near the sacroilial joints, and the rest of the spine
  • Safe sex - measures taken to reduce the risk of acquiring a sexually transmitted disease, such as the use of a condom
  • Saline - a salt solution or any substance that contains salt
  • Salivary glands - a group of glands that secrete saliva into the mouth
  • Salmonella - a group of bacteria; includes a species that causes food poisoning and another responsible for typhoid fever
  • Salmonellosis - infection by salmonella bacteria
  • Salpingectomy - surgical removal of one or both fallopian tubes
  • Salpingitis - inflammation of a fallopian tube
  • Salpingo-oophorectomy - the surgical removal of one or both of the fallopian tubes and one or both of the ovaries
  • Salpingography - X-ray examination of the fallopian tubes
  • Salpingolysis - removal of abnormal scar tissue between a fallopian tube and nearby tissue
  • Salpingostomy - surgical opening of a fallopian tube for drainage or removal of an obstruction
  • Sarcoidosis - a rare disease with no known cause that leads to inflammation in tissues throughout the body, including the lymph nodes, lungs, liver, skin, and eyes
  • Sarcoma - a cancer in connective tissue, fibrous tissue, or blood vessels
  • Saturated fat - fats that contain the maximum amount of hydrogen possible, such as those found in meats and dairy products; can contribute to coronary heart disease and the development of some cancers
  • Saturday night palsy - temporary paralysis of the arm after extended pressure on a nerve in the armpit
  • Scabies - a highly contagious skin disorder caused by a mite that burrows into the skin and produces an intense, itchy rash
  • Scarlet fever - an infectious childhood disease, caused by a streptococcus bacteria, that leads to a sore throat, fever, and rash
  • Schistosomiasis - infestation by a parasitic blood worm that can damage the liver, bladder, and intestines
  • Schizophrenia - a group of mental disorders characterized by abnormal thoughts, moods, and actions; sufferers have a distorted sense of reality, and a split personality (thoughts do not logically fit together)
  • Schönlein-Henoch purpura - inflammation and leakage of blood vessels, causing a rash
  • Sciatica - pain along the sciatic nerve, which runs down the length of the leg to the foot; usually caused by pressure on the nerve due to disk prolapse or a tumor, abscess, or blood clot
  • Sclera - the tough, white coating that covers and protects the inner structures of the eye
  • Scleroderma - an immune system disorder of varying degree that can affect many areas of the body
  • Sclerotherapy - treatment of varicose veins by injection of a solution that destroys them
  • Scoliosis - a condition in which the spine curves to one side and usually curves toward the opposite side in another section to compensate, producing a characteristic S shape
  • Screening - the testing of an otherwise healthy person in order to diagnose disorders at an early stage
  • Scrotum - the sac containing the testicles
  • Scurvy - a disease caused by a lack of vitamin C, characterized by weakness, bleeding and pain in joints and muscles, bleeding gums, and abnormal bone and tooth growth
  • Seasonal affective disorder syndrome - a type of depression that seems to be linked to shorter periods of daylight during the fall and winter
  • Sebaceous cyst - a swelling that occurs under the skin, most commonly on the scalp, face, ears, and genitals; although usually harmless, can grow very large and become painful if infected
  • Seborrhea - excessive oiliness of the face and scalp
  • Sebum - the oily, lubricating substance that is secreted by glands in the skin
  • Secondary - describes a disease or disorder that follows or is caused by another one
  • Sedatives - a group of drugs that have a calming effect; used to treat anxiety and pain, bring on sleep, and help relax a person before surgery
  • Seizure - sudden uncontrolled waves of electrical activity in the brain, causing involuntary movement or loss of consciousness
  • Selenium - an element needed by the body only in very small amounts that helps maintain tissue elasticity
  • Semen analysis - a procedure in which a semen sample is examined to determine the amount of sperm present, along with their shape and ability to move; commonly used in the treatment of male infertility
  • Semen - fluid released during ejaculation that contains sperm along with fluids produced by the prostate gland and the seminal vesicles
  • Seminal vesicles - two saclike glands in men that produce part of the fluid in semen
  • Seminiferous tubules - coiled tubes inside of the testicle that are the site of sperm production
  • Seminoma - a type of testicular cancer that is made up of only a single type of cell
  • Senile plaques - abnormal deposits of a protein called amyloid in the brain; characteristic of Alzheimer disease
  • Sensorineural hearing loss - deafness caused by damage to the inner ear or the nerve that conducts signals from the ear to the brain
  • Sensory nerve - nerves that carry information about the body’s senses toward the brain
  • Sensory organ - an organ that receives and relays information about the body’s senses to the brain
  • Sepsis - the infection of a wound or tissue with bacteria, causing the spread of the bacteria into the bloodstream; now also known as systemic inflammatory response syndrome caused by a microbe
  • Septal defect - a birth defect in which a hole is present in the wall that separates the left and right sides of the heart
  • Septic arthritis - joint inflammation caused by a bacterial infection
  • Septic shock - a life-threatening condition in which tissues become damaged and blood pressure drops due to bacteria multiplying and producing poisons in the blood
  • Septicemia - a life-threatening condition in which bacteria multiply in the blood and produce toxic materials; commonly known as blood poisoning; now also known as systemic inflammatory response syndrome.
  • Serotonin - a chemical that transmits nerve impulses in the brain, causes blood vessels to constrict (narrow) at sites of bleeding, and stimulates smooth muscle movement in the intestines
  • Serum - the clear, watery fluid that separates from clotted blood
  • Sex chromosomes - the X and Y chromosomes that determine a person’s gender; women normally have two X chromosomes and men normally have one X and one Y
  • Sex hormones - hormones responsible for producing sex characteristics and controlling sexual functions
  • Sex-linked disorder - a disorder that is caused by genes located on the sex chromosomes
  • Sexually transmitted disease - infections that are most commonly spread through sexual intercourse or genital contact
  • Shigellosis - a bacterial infection of the intestines, causing abdominal pain and diarrhea
  • Shin splints - pain and tenderness experienced in the lower leg as a result of damage or strain to leg muscles and tendons; usually caused by exercise
  • Shingles - a nerve infection caused by the chickenpox virus, causing areas of painful rash covered with blisters
  • Shock - a reduced flow of blood throughout the body, usually caused by severe bleeding or a weak heart; without treatment, can lead to a collapse, coma, and death
  • Shunt - an artificially constructed or an abnormal passage connecting two usually separate structures in the body
  • Sick sinus syndrome - abnormal functioning of the structure that regulates the heartbeat, causing episodes of abnormal heart rhythm
  • Sickle cell anemia - a genetic disorder in which the red blood cells are abnormal and deformed, causing anemia (reduced ability to transport oxygen in the blood) and clogging of blood vessels; bouts of fever, headache, and weakness result
  • Sickle cell trait - a less serious form of sickle cell anemia
  • Sigmoidoscopy - an examination of the rectum and the lowest part of the large intestine using a flexible viewing tube inserted through the anus
  • Silicone - a group of compounds of silicon and oxygen; commonly used as implants in cosmetic surgery because they resist body fluids and are not rejected by the body
  • Silicosis - a respiratory disease caused by inhalation of dust containing the mineral silica
  • Single photon emission computed tomography - an imaging technique in which a radioactive substance is introduced into the body and the radiation emitted by the substance is detected by a camera and is transformed into cross-sectional images by a computer
  • Sinoatrial node - the structure that regulates the heartbeat; a natural "pacemaker"
  • Sinus bradycardia - a regular heart rate of less than 60 beats per minute
  • Sinus rhythm - normal heart rhythm
  • Sinus tachycardia - a regular heart rate of over 100 beats per minute
  • Sinus - a cavity within bone or a channel that contains blood; also refers to an abnormal tract in the body
  • Sinusitis - inflammation of the lining of the cavities in the bone surrounding the nose (the sinuses), usually as a result of a bacterial infection spreading from the nose
  • Sjögren's syndrome - a condition characterized by dryness of the eyes, mouth, and vagina that tends to occur along with certain disorders of the immune system
  • Skin graft - a method of treating damaged or lost skin in which a piece of skin is taken from another area of the body and transplanted in a damaged or missing section
  • Skin patch test - a diagnostic test in which different allergens are taped to the skin to determine which causes an allergic reaction
  • Skin patch - a sticky patch attached to the surface of the skin that releases drugs into the bloodstream
  • Skin prick test - a test performed to determine a person’s sensitivity to a certain allergen by applying it to a small needle and using that needle to pierce the skin
  • Skull - the bones that form the framework of the head and enclose and protect the brain and other sensory organs
  • Sleep apnea - a condition in which breathing stops for very short periods of time during sleep
  • Sleeping sickness - an infectious disease in Africa spread by the bite of a tsetse fly that causes a fever and weakness
  • Slipped disk - the common term for disk prolapse
  • Small intestine - the long tube running from the stomach to the large intestine that is involved in digestion of foods and absorption of nutrients
  • Small-cell carcinoma - the most serious form of lung cancer
  • Smallpox - a highly contagious and often fatal viral infection that has been completely eradicated by immunization
  • Smear - a sample of cells spread across a glass slide to be examined through a microscope
  • Sodium bicarbonate - a substance used as an antacid
  • Sodium - a mineral that plays a role in the body's water balance, heart rhythm, nerve impulses, and muscle contraction; present in table salt (sodium chloride)
  • Solar plexus - the largest network of nerves in the body, located behind the stomach
  • Somatic - pertaining to the body
  • Spasm - an involuntary muscle contraction; can sometimes be powerful and painful
  • Spastic paralysis - spasticity involving partial paralysis
  • Spasticity - muscle stiffness caused by an increase in contractions of the muscle fibers
  • Speculum - an instrument that holds an opening of the body open so that an examination can be performed or a sample can be taken
  • Speech therapy - treatment to help someone overcome a problem communicating verbally
  • Sperm antibody - an antibody against sperm that can be produced by a woman’s immune system
  • Sperm count - the amount of normally functioning sperm per some unit of semen; used to determine a man's fertility
  • Sperm - the male sex cell produced in the testicles
  • Spermatocele - a harmless cyst containing fluid and sperm that occurs in the tube through which sperm travel from the testicles
  • Spermicide - a contraceptive substance that kills sperm
  • Sphincter - a ring of muscle fibers located around a naturally occurring passage or opening in the body that opens and closes to regulate passage of substances
  • Sphygmomanometer - an instrument used to measure blood pressure
  • Spider nevus - a collection of dilated (widened) capillaries on the skin that creates a patch resembling a spider
  • Spina bifida occulta - the least dangerous form of spina bifida, in which bones in the spine fail to close but there is no protrusion of the spinal cord or its fluid cushion out of the body
  • Spina bifida - a birth defect in which a section of the baby's spine fails to develop completely, leaving the spinal cord exposed in that section
  • Spinal cord - a long tube of nerve tissue inside the spinal column, running from the brain down the length of the back inside of the spine
  • Spinal fusion - the surgical joining of two or more adjacent vertebrae using bone fragments; used to help severe back pain or prevent damage to the spinal cord
  • Spinal tap - another term for a lumbar puncture
  • Spine - the column of bones and cartilage running along the midline of the back that surrounds and protects the spinal cord and supports the head
  • Spiral fracture - a coiled break in a bone, resembling a corkscrew
  • Spirometry - a test of lung condition; a person breathes into a machine called a spirometer that measures the volume of air exhaled
  • Spleen - an organ located in the upper left abdomen behind the ribs that removes and destroys old red blood cells and helps fight infection
  • Splenectomy - surgical removal of the spleen
  • Splint - a device that is used to immobilize a part of the body
  • Splinter hemorrhage - a splinter-shaped area of bleeding under a fingernail or toenail
  • Spondylitis - inflammation of the joints between the bones of the spine
  • Spondylolisthesis - the slipping of a vertebra in the spine over the one below it
  • Spondylolysis - a disorder in which the lower part of the spine is weakened by an abnormally soft vertebra
  • Sporotrichosis - an infection with a fungus acquired through a skin wound; causes an ulcer at the site of infection and small, rounded masses of tissue near it
  • Sprain - the tearing or stretching of the ligaments in a joint, characterized by pain, swelling, and an inability to move the joint
  • Sprue - a digestive disorder in which nutrients cannot be properly absorbed from food, causing weakness and loss of weight
  • Sputum - mucus and other material produced by the lining of the respiratory tract; also called phlegm
  • Squamous cell carcinoma - a type of skin cancer arising from flat cells of the epithelium; can also affect the lungs, cervix, and esophagus
  • Stapedectomy - surgical removal of a stapes (a sound-conducting bone in the middle ear) that cannot move to transmit sound; performed to treat hearing loss caused by otosclerosis
  • Staphylococci - common bacteria that cause skin infections and a number of other disorders
  • Status asthmaticus - a life-threatening asthma attack requiring immediate treatment
  • Status epilepticus - a life-threatening succession of epileptic seizures
  • Stein-Leventhal syndrome - see Polycystic ovary syndrome
  • Stem cells - cells that give rise to the different types of blood cells
  • Stenosis - narrowing of a body passageway
  • Stent - a device used to hold tissues in place, such as to support a skin graft
  • Stereotaxic surgery - brain surgery done through a small opening in the skull and guided by X-rays or computer-aided imaging techniques
  • Sterilization - a surgery performed to make a person incapable of reproducing; also refers to the process of killing microorganisms on objects such as surgical instruments
  • Sternum - the long, flat bone located at the center of the chest
  • Steroids - a group of drugs that includes corticosteroids, which resemble hormones produced by the adrenal glands, and anabolic steroids, which are similar to the hormones produced by the male sex organs
  • Stillbirth - a baby that is born dead after the 28th week of pregnancy; also called late fetal death
  • Stoma - a surgically formed opening on a body surface
  • Stomach bypass - a surgical procedure to treat an obstructed stomach or severe obesity in which the passage of food is diverted around the stomach and directly into the small intestine
  • Stomach stapling - a procedure in which the stomach is made smaller by partitioning it off using metal staples; used as an extreme treatment of severe obesity
  • Stool - another term for feces
  • Strabismus - a condition in which the eyes are not aligned correctly, such as cross-eye (one eye points inward) and walleye (one eye points outward)
  • Straight-leg raising - a simple test performed in a doctor’s office to check for disk prolapse
  • Strain - muscle damage resulting from excessive stretching or forceful contraction
  • Strangulated hernia - a hernia in which the protruding organ or tissue loses its blood supply, requiring emergency surgery
  • Strawberry nevus - a bright red, raised birthmark that usually disappears without treatment
  • Strep throat - a throat infection caused by streptococcus bacteria; characterized by a sore throat, fever, and enlarged lymph nodes in the neck
  • Streptococci - bacteria that cause a variety of diseases, including pneumonia and strep throat
  • Stress fracture - a bone break resulting from repeated pressure on the bone
  • Stretch marks - lines on the skin that occur when the inner skin layer is stretched thin and loses its elasticity
  • Stroke - damage to part of the brain because of a lack of blood supply (due to a blockage in an artery) or the rupturing of a blood vessel; leads to complete or partial loss of function in the area of the body that is controlled by the damaged part of the brain
  • Stye - a pus-filled abscess in the follicle of an eyelash; caused by a bacterial infection
  • Subcutaneous - a medical term meaning "beneath the skin"
  • Submucosa - the layer of connective tissue under a mucous membrane
  • Suction lipectomy - see Liposuction
  • Sudden infant death syndrome - the unexpected, sudden death of an apparently healthy baby, the cause of which cannot be found; also called crib death
  • Suppository - a solid cone or bullet-shaped object made up of a chemically inactive substance and a drug that is inserted into the rectum or vagina; used to administer a drug
  • Suppuration - the production of pus
  • Surfactant - a mixture of substances secreted by the air sacs of the lungs that prevents the air sacs from collapsing during exhalation
  • Surrogate - a woman who agrees to become pregnant and give her baby to someone else when the child is born
  • Suture - a surgical stitch that helps close an incision or wound so that it can heal properly
  • Sweat glands - tiny structures in the skin that secrete sweat
  • Sweat test - a measure of the saltiness of sweat to help diagnose cystic fibrosis
  • Swimmer's ear - see Otitis externa
  • Sycosis barbae - a bacterial infection of the hair follicles in the beard area
  • Sympathetic nervous system - the part of the autonomic nervous system that raises blood pressure and heart rate in response to stress
  • Syndactyly - a condition in which fingers or toes are fused together
  • Syndrome - a group of symptoms that indicate a certain disorder when they occur together
  • Synovectomy - surgical removal of the synovial membrane
  • Synovial fluid - a lubricating fluid secreted by the synovial membrane
  • Synovial membrane - the thin membrane that lines the inside of a joint capsule
  • Synovitus - inflammation of the membrane lining a joint capsule as a result of injury or infection or due to a chronic illness such as rheumatoid arthritis; characterized by redness, swelling, stiffness, and pain
  • Syphilis - a sexually transmitted disease; initially causes only painless sores on the genitals but can be life-threatening if untreated
  • Systemic inflammatory response syndrome - a condition characterized by having two of the following four clinical criteria: fever, rapid breathing, increased heart rate, and abnormal white blood cell count
  • Systemic lupus erythematosus - a disease of the immune system that causes inflammation of connective tissue in many areas of the body, including the skin, lungs, heart, joints, and kidneys
  • Systemic - affecting the whole body
  • Systolic pressure - the blood pressure measured while the heart is contracting
  • T cell - see T-lymphocyte
  • T-cell leukemia - a type of leukemia caused by a virus in which T-lymphocytes divide uncontrollably
  • T-lymphocyte killer cell - a type of T-lymphocyte white blood cell that attaches to abnormal cells and releases chemicals that destroy them
  • T-lymphocyte - a type of white blood cell that fights infections and destroys abnormal cells directly; as compared with releasing antibodies to fight infection
  • TB - see Tuberculosis
  • TENS - see Transcutaneous electrical nerve stimulation
  • TIA - see Transient ischemic attack
  • TMJ syndrome - see Temporomandibular joint syndrome
  • TPA - see Tissue plasminogen activator
  • Tachycardia - a rapid heart rate (over 100 beats per minute)
  • Tapeworm - a parasitic worm that lives in the intestines; causes diarrhea and abdominal discomfort
  • Tar - the sticky, brown substance in cigarettes that coats the lungs; causes lung and other cancers
  • Tarsorrhaphy - a procedure in which the eyelids are sewn shut; performed to protect the corneas
  • Tartar - the hard deposit formed on teeth when mineral salts in saliva combine with plaque; can cause dental problems such as gum disease if not controlled
  • Tay-Sachs disease - a severe genetic disorder that causes nervous system disturbances and death, usually before the age of 3
  • Tear duct - a tiny passageway that drains lubricating tears from the surface of the eye to the back of the nose
  • Telangiectasia - redness of an area of skin, caused by enlargement and proliferation of the underlying small blood vessels
  • Temperature method - a natural method of family planning in which a woman determines her time of ovulation by changes in her daily temperature
  • Temporal arteritis - inflammation and narrowing of arteries in the head and neck, including those in the scalp near the temple, which can cause blindness if untreated
  • Temporomandibular joint syndrome - headache, facial pain, and jaw tenderness caused by irregularities in the way the joints, muscles, and ligaments in the jaw work together
  • Tendinitis - inflammation of a tendon, usually caused by injury, characterized by pain, tenderness, and sometimes limited movement in the attached muscle
  • Tendon transfer - surgical cutting and repositioning of a tendon so that the muscle attached to it has a new function
  • Tendon - strong connective tissue cords that attach muscle to bone or muscle to muscle
  • Tennis elbow - a form of tendinitis that causes pain and tenderness in the elbow and forearm
  • Tenosynovitis - inflammation of the inner lining of the sheath that covers a tendon
  • Tenovaginitis - inflammation of the fibrous wall of the sheath that covers a tendon
  • Tension headache - a headache caused by emotional strain or tension in the muscles of the head and neck
  • Teratogen - anything that causes abnormalities in a developing embryo or fetus, such as a drug or virus
  • Teratoma - a tumor composed of cells not normally found in the part of the body when the tumor occurred
  • Termination of pregnancy - see Abortion
  • Testicles - the two male sex organs that produce sperm and the sex hormone testosterone
  • Testicular feminization factor - a genetic disorder in which an individual who is genetically male has the external appearance of a female because the body is unresponsive to testosterone
  • Testicular torsion - severe pain and swelling of a testicle, due to twisting of the spermatic cord
  • Testosterone - the sex hormone that stimulates development of male sex characteristics and bone and muscle growth; produced by the testicles and in small amounts by the ovaries
  • Tetanus - a sometimes fatal disease affecting the brain and spinal cord; caused by infection with bacterium present in soil and manure
  • Tetracyclines - a group of antibiotic drugs used to treat a wide variety of infections, including bronchitis and some types of pneumonia
  • Tetralogy of Fallot - a genetic heart disease involving four structural defects in the heart, which result in insufficient levels of oxygen in the blood
  • Thalamus - a structure in the brain that relays and processes incoming sensory information from the eyes and ears and from pressure and pain receptors
  • Thalassemia - a group of genetic blood disorders characterized by a defect in the ability to produce hemoglobin, leading to the rupturing of red blood cells (called hemolytic anemia)
  • Thallium scanning - a type of radionuclide scanning used to assess the heart
  • Therapeutic range - the range of doses of a drug that will produce beneficial results without side effects
  • Thoracoscopy - examination of the membranes covering the lungs using an endoscope
  • Thoracotomy - a procedure in which the chest is surgically opened to operate on an organ in the chest cavity
  • Thorax - the chest
  • Thrill - a vibration felt when the hand is placed flat on the chest; caused by abnormal blood flow through the heart as a result of disease
  • Thrombectomy - removal of a blood clot
  • Thrombocytopenic purpura - a decrease in the number of platelets in the blood, causing abnormal bleeding of blood vessels into the skin
  • Thromboembolism - blockage of a blood vessel by a blood clot fragment that has broken off and traveled from another area of the body
  • Thrombophlebitis - inflammation of a vein, along with clot formation in the affected area
  • Thrombosis - a condition in which a blood clot (thrombus) has formed inside a blood vessel
  • Thrombus - a blood clot in a blood vessel
  • Thrush - a candidiasis infection
  • Thymoma - a tumor of the thymus gland
  • Thymus gland - an immune system gland located in the upper part of the chest that plays an important role in the production of T-lymphocytes
  • Thyroglossal cyst - a swelling at the front of the neck; forms from a duct that fails to disappear during embryonic development
  • Thyroid gland - a gland located in the front of the neck below the voice box that plays an important role in metabolism (the chemical processes in the body) and growth; the gland produces thyroid hormone
  • Thyroiditis - inflammation of the thyroid gland
  • Thyrotoxicosis - a toxic condition resulting from overactivity of the thyroid gland
  • Thyroxin - a hormone produced by the thyroid gland that helps regulate energy production in the body
  • Tibia - the thicker of the two long bones in the lower leg; commonly called the shin
  • Tic douloureux - see Trigeminal neuralgia
  • Tic - an involuntary, repetitive movement such as a twitch
  • Ticks - small, eight-legged animals that can attach to humans and animals and feed on blood; sometimes spread infectious organisms via their bites
  • Tietze's syndrome - inflammation of the cartilage that joins ribs to the breastbone, causing chest pain
  • Tinea - a group of common infections occurring on the skin, hair, and nails that are caused by a fungus; commonly referred to as ringworm
  • Tinnitus - a persistent ringing or buzzing sound in the ear
  • Tipped uterus - an abnormal condition in which the uterus is tilted backward instead of slightly forward
  • Tissue plasminogen activator - a substance produced by the body and as a genetically engineered drug to prevent abnormal blood clotting
  • Tissue typing - tests used to determine the compatibility of tissues used in grafts and transplants
  • Tolerance - decreased sensitivity of the body to a certain drug, usually either because the liver becomes more efficient at breaking down the drug or the body's tissues become less sensitive to it; increased tolerance creates a need for a higher dose of the drug in order to have the same effects
  • Tonometry - the procedure used to measure the pressure within the eye; is useful in detecting glaucoma
  • Tonsillectomy - surgical removal of the tonsils, usually to treat tonsillitis
  • Tonsillitis - infection and inflammation of the tonsils
  • Tonsils - masses of lymphoid tissue located at either side of the back of the throat
  • Tourette's syndrome - a movement disorder characterized by involuntary tics and noises, and in some cases uncontrollable shouting of obscenities
  • Tourniquet - a device placed tightly around an arm or leg in order to stop blood flow; can be used to locate veins in order to take a blood sample or to control blood flow during some operations
  • Toxemia - the presence of bacterial toxins in the blood
  • Toxic epidermal necrolysis - a severe rash in which the outer layers of skin blister and peel off
  • Toxic shock syndrome - a life-threatening condition caused by a staphylococci toxin
  • Toxicity - the extent to which a substance is poisonous
  • Toxin - a poisonous substance
  • Toxocariasis - human infestation with the larvae of a worm found in the intestines of dogs
  • Toxoplasmosis - a common protozoan infection that is usually only dangerous to a fetus in early pregnancy or a person who is immunocompromised
  • Trachea - the tube running from the larynx (the voice box) down the neck and into the upper part of the chest, where it divides to form the two bronchi of the lungs; commonly called the windpipe
  • Tracheitis - inflammation of the trachea
  • Tracheotomy - insertion of a tube through a surgical opening in the trachea to maintain an open airway
  • Trachoma - a persistent, contagious form of conjunctivitis that can lead to complications such as blindness if untreated
  • Traction - the use of tension to hold a body part in place or to correct or prevent an alignment problem
  • Transcutaneous electrical nerve stimulation - a method of relieving pain by applying tiny electrical impulses to nerve endings beneath the skin
  • Transcutaneous - through the skin
  • Transferrin - a substance in the blood that transports iron throughout the body
  • Transient ischemic attack - a temporary block in the supply of blood to the brain, resulting in temporary loss of sensation, movement, vision, or speech; often called ministrokes and can be precursors to a real stroke
  • Transmissible - able to be passed from one organism to another
  • Transplant - transferring a healthy tissue or organ to replace a damaged tissue or organ; also refers to the tissue or organ transplanted
  • Transurethral prostatectomy - removal of cancerous tissue from the prostate gland using a resectoscope (a long, narrow instrument passed up the urethra), which allows the surgeon to simultaneously view the prostate and cut away the cancerous tissue
  • Trauma - physical injury or emotional shock
  • Travelers' diarrhea - diarrhea when traveling in a foreign country, caused by contaminated food or water
  • Tremor - an involuntary, rhythmic, shaking movement caused by alternating contraction and relaxation of muscles; can be the normal result of age or the abnormal effect of a disorder
  • Triage - a system used to classify sick or injured people according to the severity of their conditions
  • Trichiasis - growth of the eyelashes inward toward the cornea, causing persistent irritation of the eyeball
  • Trichinosis - infestation by the larvae of the parasitic worm Trichinella spiralis, usually acquired by eating undercooked pork
  • Trichomoniasis - infection of the vagina by the single-celled parasite Trichomonas vaginilis, which may cause inflammation, itchiness, and discharge from the vagina
  • Tricuspid valve - the valve located between the two left chambers of the heart (the left atrium and the left ventricle)
  • Tricyclic antidepressants - drugs used in the treatment of clinical depression
  • Trigeminal neuralgia - a disorder of the trigeminal nerve (a cranial nerve) that causes brief attacks of severe pain in the lips, cheeks, gums, or chin on one side of the face
  • Triglyceride - the main form of fat in the blood; determining levels of triglyceride is useful in diagnosing and treating diabetes, high blood pressure, and heart disease
  • Trimester - one of three periods lasting about 3 months each; the stages into which pregnancy is divided
  • Triple X syndrome - the presence of an extra X chromosome in a woman, which may cause some degree of mental retardation
  • Trismus - the medical term for lockjaw
  • Trisomy 21 - see Down syndrome
  • Trisomy - the presence in the cells of three copies of a certain chromosome instead of the normal two copies
  • Tubal ligation - a procedure in which the fallopian tubes are cut and tied off; usually a permanent form of sterilization
  • Tubal pregnancy - a pregnancy that occurs in the fallopian tubes, with a fertilized egg implanting in the tube instead of the uterus; severely painful and can be fatal if not detected and treated
  • Tuberculin test - skin tests performed to determine previous infection with tuberculosis; can help rule out the possibility of being currently infected with tuberculosis
  • Tuberculosis - an infectious bacterial disease transmitted through the air that mainly affects the lungs
  • Tuberous sclerosis - a genetic disorder of the skin and nervous system characterized by epilepsy, mental retardation, and a skin condition resembling acne
  • Tuboplasty - surgical repair of a damaged fallopian tube to treat infertility
  • Tumor - an abnormal mass that occurs when cells in a certain area reproduce unchecked; can be cancerous (malignant) or noncancerous (benign)
  • Tunnel vision - loss of peripheral vision so that only objects directly ahead can be seen; most commonly due to damage caused by increased pressure within the eye (glaucoma)
  • Turner's syndrome - a genetic disorder in women in which only one X chromosome is present, or both chromosomes are present but one is defective
  • Tympanic membrane - the medical term for the eardrum
  • Tympanoplasty - a surgical procedure used to treat hearing loss in which the eardrum or structures in the middle ear are repaired
  • Typhoid fever - an acute bacterial infection causing fever, headache, abdominal discomfort, and enlargement of the liver and spleen
  • Typhus - a group of diseases caused by the microorganism rickettsia, spread by the bites of fleas, mites, or ticks; symptoms include headache, fever, rash, and a series of complications if untreated
  • Ulcer - an open sore that occurs on the skin or on a mucous membrane because of the destruction of surface tissue
  • Ulcerative colitis - a chronic condition in which ulcers occur on the mucous membrane lining of the colon (the end of the large intestine) and the rectum
  • Ultrasound scanning - an imaging procedure used to examine internal organs in which high-frequency sound waves are passed into the body, reflected back, and used to build an image; also sometimes called sonography
  • Ultraviolet light - a form of invisible light in sunlight that is responsible for the tanning and burning of skin and can cause cataracts and skin cancer
  • Umbilical cord - the tubal structure (consisting of two arteries and one vein) that connects the fetus to the placenta, supplying the fetus with oxygen and nutrients and removing some waste products
  • Umbilical hernia - a condition present at birth in which a part of the baby's intestines bulge through a weak area of the abdominal wall, creating a swelling around the navel
  • Unconsciousness - a temporary or prolonged loss of awareness of self and of surroundings
  • Undescended testicle - a testicle that has not moved down from the abdomen, where it develops, into the scrotum
  • Unsaturated fat - a fat or oil found mainly in vegetables; thought to reduce the risk of coronary heart disease
  • Urea - a waste product of the metabolism of proteins that is formed by the liver and secreted by the kidneys
  • Uremia - abnormally high levels of waste products such as urea in the blood
  • Ureters - two tubes that carry urine from the kidneys to the bladder
  • Urethra - the tube by which urine is released from the bladder
  • Urethritis - inflammation of the urethra
  • Urethrocele - a bulging of the urethra into the vagina
  • Urethrocystitis - inflammation of the urethra and the bladder
  • Urinalysis - a group of physical and chemical tests done on a sample of urine to check for various disorders, including those of the kidneys and urinary tract
  • Urinary diversion - an operation to allow urine passage when the bladder or urethra has become blocked or been removed
  • Urinary incontinence - the involuntary release of urine because of the inability to control bladder muscles; may occur as a natural part of the aging process or be caused by an injury or disorder
  • Urinary tract - the structures in the body that are responsible for the production and release of urine, including the kidneys, ureters, bladder, and urethra
  • Urticaria - an allergic reaction in which itchy white lumps surrounded by areas of inflammation appear on the skin; commonly called "hives"
  • Uterine prolapse - a condition in which the uterus moves downward into the vagina due to a weakness of the ligaments and muscles that hold the uterus in place
  • Uterus - the hollow female reproductive organ in which a fertilized egg is implanted and a fetus develops
  • Uvea - a structure consisting of the colored area of the eye and the middle layer of the eye that contains blood vessels
  • Uveitis - inflammation of the uvea
  • V/Q lung scans - images produced by radionuclide scanning of the lungs; used to help diagnose a pulmonary embolism
  • VD - see Venereal disease
  • VLDL - see Very low-density lipoprotein
  • Vaccination - a form of immunization in which killed or weakened microorganisms are placed into the body, where antibodies against them are developed; if the same types of microorganisms enter the body again, they will be destroyed by the antibodies
  • Vaccine - a preparation of weakened microorganisms given to create resistance to a certain disease
  • Vacuum aspiration - removal of the contents of the uterus using a suction device
  • Vacuum extraction - a technique used to facilitate childbirth using a suction device to help move the baby through the birth canal
  • Vagina - the muscular passage connecting the uterus with the outside genitals; a component of the female reproductive system
  • Vaginismus - an involuntary muscle spasm at the opening of the vagina when sexual intercourse is attempted; can be quite painful and may make sexual intercourse nearly impossible
  • Vaginitis - inflammation of the vagina, which can be the result of infection, aging, a hormone deficiency, or a foreign object (such as a tampon)
  • Valve - a structure that allows fluid flow in only one direction
  • Valvotomy - surgical correction of a narrowed heart valve
  • Valvular heart disease - a heart valve defect
  • Valvuloplasty - reconstruction or repair of a narrowed heart valve
  • Varicella - the medical term for chickenpox
  • Varices - enlarged or twisted blood or lymph vessels
  • Varicocele - the appearance of varicose veins around the testicles; commonly occurs and is harmless, but may cause discomfort
  • Varicose veins - enlarged, twisted veins just below the surface of the skin, caused by defective valves in the veins
  • Variola - another term for smallpox
  • Vas deferens - a thin tube that stores and transports sperm
  • Vascular - pertaining to blood vessels
  • Vasculitis - inflammation of blood vessels
  • Vasectomy - a usually permanent method of sterilization in which the tubes carrying sperm from the testicles (the vas deferens) are cut and tied off; as a result, the semen will no longer contain sperm
  • Vasoconstriction - narrowing of blood vessels
  • Vasodilation - widening of blood vessels
  • Vasovagal attack - a sudden slowing of the heart, causing fainting
  • Vein - a blood vessel that carries blood toward the heart
  • Venereal disease - any disease that is usually spread through sexual intercourse or genital contact
  • Venipuncture - piercing of a vein with a hollow needle to inject fluid or withdraw blood
  • Venography - an X-ray procedure for viewing veins
  • Venom - a poisonous substance produced by certain animals
  • Ventilation - the process through which oxygen and carbon dioxide are exchanged between the lungs and the air; also refers to the use of a machine to carry out this process in someone who cannot breathe on his or her own
  • Ventilator - a machine used to take over breathing when a person cannot breathe on his or her own
  • Ventricle - a small cavity or chamber; there are four ventricles in the brain that circulate cerebrospinal fluid through it, and two in the heart that pump blood throughout the body
  • Ventricular fibrillation - rapid, irregular contractions of the heart
  • Ventricular septal defect - a hole in the wall that separates the two lower chambers of the heart (called the ventricles)
  • Vernix - the thick, greasy substance that covers the skin of a newborn baby
  • Version - a shift in the position of the fetus inside of the uterus, either occurring naturally or as performed by a doctor to facilitate delivery
  • Vertebra - any one of the 33 bones that make up the spine
  • Vertebral arteries - a pair of arteries running up the neck to supply the brain with blood
  • Vertebrobasilar insufficiency - episodes of dizziness and weakness caused by insufficient blood flow to the brain
  • Vertex presentation - the usual, head-first presentation of the fetus during delivery
  • Vertigo - the feeling that one or one's surroundings are spinning
  • Very low-density lipoprotein - a class of blood proteins, a high level of which is associated with coronary heart disease
  • Vesicle - a small skin blister, or any sac in the body, that contains fluid
  • Vestibular glands - two small glands located at the opening of the vagina that secrete a lubricating fluid during sexual stimulation
  • Villi - the millions of fingerlike projections on the lining of the small intestine that aid in the absorption of food
  • Viral - a term describing something related to or caused by a virus
  • Viremia - the presence of viruses in the blood
  • Virilization - the process by which a woman develops male characteristics; caused by overproduction of male sex hormones
  • Virulence - the relative ability of an organism to cause disease
  • Virus - the smallest known disease-causing microorganism; viruses are very simple in structure and can only multiply when they are inside the cell of another organism
  • Visual acuity - a measure of the sharpness of a person's vision
  • Visual field - the area on both sides that can be seen while looking straight ahead
  • Vital sign - any sign, such as a pulse, that indicates that a person is alive
  • Vitamin A - a vitamin essential for normal growth and development of the body (most notably the bones and teeth), protection of mucous membranes from infection, normal vision, and healthy skin and hair
  • Vitamin B complex - a group of vitamins including thiamine, niacin, riboflavin, pantothenic acid, pyridoxine, biotin, and folic acid; plays a variety of important roles in the body, including in hormone production, metabolism, and functioning of the nerves, muscle, heart, and digestive system
  • Vitamin B12 - a vitamin that is essential to the production of DNA (the genetic material in cells) and red blood cells and in the functioning of the nervous system
  • Vitamin B6 - a vitamin that plays an important role in the breakdown and use of energy sources, production of red blood cells and antibodies, and normal functioning of the nervous system
  • Vitamin C - a vitamin with many essential roles, including in maintaining healthy bones, teeth, gums, ligaments, and blood vessels and in the immune system's response to infection
  • Vitamin D - a vitamin that plays a role in the absorption of calcium by the intestines and is essential for healthy bones and teeth
  • Vitamin E - a vitamin that protects tissues from damage by oxygen free radicals, helps to form red blood cells, maintains the function of enzymes, and maintains cell structure
  • Vitamin K - a vitamin that is essential for normal blood clotting and the body's absorption of calcium
  • Vitamins - complex substances that are necessary in small amounts to maintain health and ensure proper development and functioning of the body
  • Vitiligo - a condition in which patches of skin on the body lose their color; thought to be caused by the immune system attacking the skin tissues, causing the absence of melanin
  • Vitreous humor - the clear, watery fluid that fills the cavity of the eye behind the lens
  • Vocal cords - two strips of tissue in the voice box that have the ability to produce sound when air passing through them causes the tissues to vibrate
  • Volvulus - twisting and obstruction of an area of intestine
  • Von Willebrand's disease - a genetic disorder characterized by excessive bleeding
  • Vulva - the outer, visible portion of the female genitals
  • Vulvitis - inflammation of the vulva
  • Vulvovaginitis - inflammation of the vulva and vagina
  • Walleye - a condition in which one eye turns outward
  • Wart - a contagious, harmless growth caused by a virus that occurs on the skin or a mucous membrane
  • Weber's test - a test in which a vibrating tuning fork is held against the forehead to help determine the cause of hearing loss
  • Wegener's granulomatosis - a disorder in which nodules associated with inflammation of blood vessels develop in the lungs, kidneys, and nasal passageways
  • Weight-bearing exercise - exercise that puts stress on bones, such as walking, which helps build up bone density and prevent the bones from becoming brittle
  • Wernicke's encephalopathy - a brain disorder characterized by abnormal eye movements, difficulties with muscle coordination, and confusion; usually the result of chronic alcoholism
  • Wheeze - a high-pitched sound produced during breathing because of narrowing of the airways; common sign of asthma
  • Whiplash injury - injury to the ligaments, joints, and soft tissues of the neck region of the spine because of a sudden, violent jerking motion of the head
  • Whipple's disease - a rare disorder that has widespread effects on the body, including impaired absorption of nutrients, weight loss, joint pain, and anemia
  • Whipworm - a small, parasitic worm that can live in the intestines of a human and may cause diarrhea, abdominal pain, and anemia
  • White blood cell count - the number of white blood cells present in a blood sample; useful in diagnosing and evaluating various diseases and infections
  • White blood cell - a group of colorless blood cells that are part of the immune system, helping prevent and fight infection
  • Whitehead - a painless, small, white bump; usually occurs in groups on the nose, cheeks, or around the eyes
  • Whitlow - an abscess on the end of a finger or a toe that is caused by the herpes simplex virus or a bacterial infection
  • Whooping cough - see Pertussis
  • Wilm's tumor - a type of kidney cancer that usually affects children under the age of 5
  • Wilson's disease - a rare genetic disorder in which copper builds up in the liver and is released into other parts of the body, eventually causing damage to the liver and brain
  • Withdrawal bleeding - bleeding from the vagina that occurs when hormone levels drop, such as menstruation or the bleeding that occurs at the end of each cycle of the combined oral contraceptive pill
  • X chromosome - one of the two sex chromosomes; determines female sex characteristics
  • X-linked disorder - a genetic disorder in which the abnormal gene is located on the X chromosome; those affected are almost always men
  • X-ray - see Radiography
  • XYY syndrome - a disorder in which a man has an extra Y chromosome, causing him to be unusually tall and to have behavioral disorders
  • Xanthelasma - fatty deposits around the eyes that are common in elderly people and are associated with high levels of cholesterol in the blood
  • Xanthine - a bronchodilator drug that is used to treat asthma
  • Xanthomatosis - a condition in which fatty deposits occur in various parts of the body, possibly leading to atherosclerosis
  • Xeroderma pigmentosum - a genetic disorder in which the skin is extremely sensitive to sunlight, causing it to age prematurely and leaving the individual particularly susceptible to skin cancer
  • Xerophthalmia - excessive dryness of the cornea and conjunctiva due to a lack of vitamin A
  • Y chromosome - one of the two sex chromosomes; determines male sex characteristics
  • Yeast infection - a term usually referring to a candidiasis infection
  • Yellow fever - a life-threatening viral infection transmitted by mosquitoes that causes jaundice, fever, headache, and vomiting
  • ZIFT - see Zygote intrafallopian transfer
  • Zinc chloride - a white powder used as an antiseptic and antiperspirant
  • Zollinger-Ellison syndrome - a rare disorder in which tumors form in the pancreas and secrete the hormone gastrin, which causes increased production of gastric acid and recurrent peptic ulcers
  • Zoonosis - a parasite-caused or infectious disease in animals that can be transferred to humans
  • Zygote intrafallopian transfer - a method used to treat infertility in which an egg fertilized outside the body is placed into a woman's fallopian tube
  • Zygote - the cell that results when an egg is fertilized by a sperm
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